Insert for compression mould punch

Abstract

A punch is disclosed for a compression moulding unit for compression-moulding plastics for forming capsules, in which the punch comprises a stem and an insert, the insert comprises a head portion and a stem portion, the head portion comprises a front surface intended to come into compression contact with the plastics, the stem portion has an inner cavity into which an end portion of the stem is inserted which is cylindrical in shape coupling, the stem portion is fixed to the end portion by two removable locking pins; the insert is interchangeable and the axis of the assembled punch is centred with precision with respect to the compression axis of the moulding unit without finishing machining subsequent to fitting the insert in the stem.

Description

Insert for Compression Mould PunchBackground of the invention

[0001] The invention relates to an insert that is usable for making a punch for compression moulding, a punch provided with the aforesaid insert, a moulding unit provided with the aforesaid punch, a moulding device provided with a plurality of moulding units, and a use of the aforesaid insert to make a punch and perform compression moulding. Punch means the male portion of a compression mould configured to mould material in a forming cavity defined between the male portion and a female portion, or die, of the mould.

[0002] Specifically, but not exclusively, the invention can be applied to compression moulding doses of plastics, in particular for forming capsules for closing containers.

[0003] In particular, reference is made to an insert made according to the preamble of the first claim. Such an insert is disclosed, for example, in patent publication WO 2018 / 015834 Al, which shows a punch for compression moulding plastics for forming capsules for closing containers, in which the punch comprises a stem, an insert with a head portion and a stem portion screwed to the stem, and a channel formed inside the head portion and communicating with a gas conduit arranged in the interface between the insert and the stem and configured to enable gas to be extracted from / injected into the forming cavity.

[0004] In the mould disclosed in WO 2018 / 015834 Al, the axis of the punch is centered with respect to the compression axis of the mould mainly by precision cylindrical coupling between one or more outer cylindrical surfaces of the stem of the punch and respective inner cylindrical surfaces of a seat of the mould within which the punch is axially slidable.

[0005] Precise cylindrical sliding coupling between another inner cylindrical surface of the seat of the mould and an outer cylindrical surface arranged on the head portion of the insert contributes to centering.

[0006] One of the advantages of this solution is the interchangeability of the insert. Replacing the insert can be useful, for example, in the case of wear to the insert, or for a machining change, or for still other reasons.

[0007] One drawback of the mould disclosed in WO 2018 / 015834 Al is the need to perform, when first fitting an insert to the stem of the punch, and every time a new insert is fitted, a high precision finishing machining task to ensure that the punch components arecoaxial and that the punch is thus perfectly centered in the mould with respect to the compression axis.

[0008] The prior art further comprises patent publication CN 212860111 U, which shows an insert with a head portion and a stem portion, in which the stem portion of the insert has an outer frustoconical surface configured for coupling with an inner frustoconical surface of a stem by two positioning and locking pins each of which is inserted into two respective coaligned holes formed on the stem and into a respective slot formed on the stem portion of the insert, to ensure coaxiality between insert and stem.

[0009] One of the drawbacks of this second solution is the need to manufacture an insert with high mechanical precision, otherwise the coupling between the insert and the stem becomes problematic, uncertain and defective, if not impossible to achieve, as also a minimal error in the conformation and / or in the arrangement of the frustoconical surface of the stem portion of the insert could cause a positioning and coupling error with the stem, for example a misalignment between the holes on the stem and the slot on the insert, with resulting difficulty in inserting the positioning and locking pin.

[0010] Another undesired consequence of an even minimal geometric error in the manufacture of the conjugate frustoconical surfaces of the solution disclosed in CN 212860111 U is the risk of obtaining an undesired situation in which, although the positioning and locking pins are inserted between the insert and the stem, correct axial abutment interaction between the abutment surfaces of the insert and of the stem could be absent, so that sufficient stability and reliability of the axial position of the insert with respect to the stem would not be guaranteed

[0011] It is clear that in the solution disclosed in CN 212860111 U, high manufacturing precision, in particular of the parts that determine the reciprocal positioning between the insert and the stem and influence coupling correctness, is a necessary condition for making the insert actually interchangeable. In other words, in order to be usable for inserting into the punch, all the interchangeable inserts must be constructed with extremely high precision.Summary of the invention

[0012] One object of the invention is to remedy one or more of the aforesaid limits and drawbacks of the prior art.

[0013] One object of the invention is to provide an insert for a punch and / or a punch that are alternatives to those of the prior art.

[0014] One advantage is to make an insert that is usable to assemble a punch for a compression mould.

[0015] One advantage is to provide a punch that is provided with an interchangeable insert that is pretty fast and easy to replace.

[0016] One advantage is to construct a punch by assembling an insert with a stem, without the need for machining, after assembly, to ensure precise centering of the punch on the compression axis of the mould.

[0017] One advantage is to make available a punch assembled with an insert that is easily interchangeably and with a significantly precise construction.

[0018] One advantage is to obtain a compression punch by a relatively simple and cheap manufacturing process.

[0019] One advantage is to create a compression punch with relatively high stiffness and which for this reason is particularly suitable for moulding workpieces in which great precision in form and dimensions is required.

[0020] One advantage is to ensure precise and effective moulding of workpieces (capsules for closing containers) comprising a particularly thin wall (in particular a bottom wall, for example the panel of a capsule).

[0021] One advantage is to simplify and facilitate replacing the for example worn or damaged insert, without replacing the rest of the punch.

[0022] Such objects and advantages and still others are achieved by an insert for a punch and / or by a punch and / or by a moulding unit and / or by a forming device and / or by a use of an insert, according to one or more of the claims set out below.

[0023] In one embodiment, a material compression moulding unit, in particular of plastics, comprises a punch; the punch comprises a stem and an insert; the insert comprises a head portion and a stem portion; the head portion comprises a front surface configured for compression contact with the material; the stem portion has a cavity into which an end portion of the stem with a cylindrical-shaped coupling is inserted; the stem portion is fixed to the end portion by one or more locking pins; the stem portion comprises an outer surface that is couplable with precision centering to a corresponding inner surface of the moulding unit with the possibility of axial sliding along a compression axis.Brief description of the drawings

[0024] The invention can be better understood and implemented with reference to the appended drawings, which illustrate some embodiments by way of non-limiting example,in which:Figure 1 is a perspective view of a first embodiment of a punch insert made in accordance with the present invention;Figure 2 is a top view of the insert of Figure 1;Figure 3 is an exploded view of an assembly station for assembling a punch for compression moulding, in which the insert of Figure 1 has to be fitted to a stem to assemble the punch;Figure 4 is a partially sectioned top view of the assembly station of Figure 3, in a first assembly step in which the insert has not yet been inserted into the stem;Figure 5 is the view of Figure 4 in a second assembly step in which the insert has been inserted into the stem;Figure 6 is a partially sectioned side view in a vertical elevation of the assembly station of Figure 3 in a third assembly step in which the locking pin is about to be inserted into the punch;Figure 7 is the view of Figure 6 in a fourth assembly step in which the locking pin has been inserted into the punch;Figure 8 shows an enlarged detail of Figure 5;Figure 9 shows an enlarged detail of Figure 6;Figure 10 shows an enlarged detail of Figure 7;Figure 11 is a section in vertical elevation of a moulding unit that comprises the assembled punch of Figures 3-10;Figure 12 shows an enlarged detail of Figure 11;Figure 13 shows an enlarged detail of Figure 12;Figure 14 is a straight cross section drawn at the locking pins of a punch provided with the insert of Figure 1;Figure 15 is a longitudinal section of a second embodiment of a punch made in accordance with the present invention;Figure 16 is a schematic top view of a moulding carousel that comprises a plurality of moulding units like that in Figure 11.Detailed description

[0025] With reference to figures mentioned above, for greater clarity and simplicity of exposition, identical elements of different embodiments have been indicated by the same numbering.

[0026] With 1, an insert has been indicated that is usable as a component for assembling a punch for compression moulding material, in particular plastics. The punch provided with the insert 1 may be used, in particular, in the ambit of a compression moulding unit for compression-moulding plastics for forming capsules for closing containers.

[0027] The insert 1 comprises a body extending along a longitudinal axis X. The body comprises a head portion 2 and a stem portion 3. The body may comprise, substantially, a mushroom structure with a head and a stem. The body may be, in particular, made as a single piece.

[0028] The head portion 2 comprises a front surface 4 transverse to the longitudinal axis X. The front surface 4 may comprise, in particular, a flat or prevalently flat surface. The front surface 4 may be, in particular, circular in shape or with a circular edge. The front surface 4 may be, in particular, orthogonal to the longitudinal axis X. The front surface 4 is configured for compression contact with the material to compress. The front surface 4 is designed to define a forming cavity for compression moulding an object.

[0029] The head portion 2 comprises a first outer side surface 5 that may comprise, in particular, at least one cylindrical portion. The first outer side surface 5 is coaxial with the longitudinal axis X. In particular, the first outer side surface 5 may be cylindrical only in a portion arranged at a distance from the front surface 4, whereas another portion, nearer or contiguous with the front surface 4, may be conical or shaped.

[0030] The first outer side surface 5 has a first diameter (in particular, the diameter of the cylindrical portion, i.e. the maximum diameter of the head portion 2) and a first axial length (in particular, the total axial length of the head portion 2). The first outer side surface 5 is designed in use for axial sliding coupling inside a seat of a mould along a compression axis, as will be explained better below in the description.

[0031] The first outer side surface 5 may be, in particular, joined to the front surface 4, for example by an edge (for example a chamfered edge) or a corner (for example a rounded corner) or another type of junction (for example a junction extending circumferentially).

[0032] The stem portion 3 comprises a second outer side surface 6 of cylindrical shape. The second outer side surface 6 is coaxial with the longitudinal axis X. The second outer side surface 6 has a second diameter that is less than the first diameter. The second outer side surface 6 has a second axial length that may be, in particular, greater than the first axial length. The second axial length may be, in particular, at least more than twice, ormore than triple, the first axial length. The second axial length may be, in particular, at least more than three, or four, or five times the axial length of only the cylindrical portion of the first outer side surface 5.

[0033] The second outer side surface 6 is designed in use for an axial sliding coupling inside a seat of a mould along a compression axis, with relatively very precise coupling (with relatively very reduced radial clearance) to promote exact centering of the punch with respect to the compression axis, as will be explained better below in the description.

[0034] The stem portion 3 comprises inside a cavity 7 that extends axially and has an end opening arranged on a side of the body opposite the side where the front surface 4 of the head portion 2 is located.

[0035] The stem portion 3 comprises an inner side surface 8 of cylindrical shape that defines, at least partially, the aforesaid cavity 7. The inner side surface 8 is coaxial with the longitudinal axis X. The inner side surface 8 has an inner diameter that is smaller than the second diameter.

[0036] The inner side surface 8 is designed in use for cylindrical in shape coupling with an end portion of another component (stem) of the punch, as will be explained better below in the description.

[0037] At least one hole 9 is formed on the stem portion 3 (in this specific embodiment a further hole 9 is provided) with a hole axis transverse to the longitudinal axis X. The two holes 9 are arranged alongside one another. Each hole 9 is configured to receive a respective locking pin 10 for coupling the insert 1 with an element that is able to receive the insert (in the specific case, the aforesaid end portion of the stem of the punch) As said, in this embodiment at least one further hole 9 with a further hole axis transverse to the longitudinal axis is formed on the stem portion 3. The further hole 9 may be, in particular, configured to receive a respective further locking pin 10. The further hole axis of the further locking pin 10 may be, in particular, parallel to the hole axis of the locking pin 10.

[0038] The second outer side surface 6 (or at least one part thereof) may be arranged, in particular, in an area comprised axially between each hole 9 and the head portion 2.

[0039] Each hole 9 extends between a first opening 11 and a second opening 12. Both the openings are arranged on an outer surface of the stem portion 3. Each hole 9 defines a recess 13 formed on an inner surface of the stem portion 3. Each recess 13 is arranged in a central part of the respective hole 9 and is configured to receive a side portion of a lockingpin inserted into the hole 9. The first opening 11 and the second opening 12 may be, in particular, arranged on a lowered area of the stem portion 3 that is recessed with respect to the second outer side surface 6, so that the second outer side surface 6 comprises, in this specific embodiment, two cylindrical surface portions that are separated axially from one another by the aforesaid lowered area and work in substantially the same manner to centre the punch with respect to the compression axis.

[0040] A diameter of the first opening 11 may be, in particular, greater than a diameter of the second opening 12, to enable the locking pin 10 to be inserted through the first opening 11 (for example, with slight forcing) and to prevent the locking pin 10 from exiting through the second opening 12 and promote correct positioning of the pin approximately in the centre of the hole 9. It is possible to extract the locking pin 10 by a tool U that passes through the second opening 12 and pushes the locking pin 10 out of the hole 9.

[0041] The stem portion 3 may comprise, in particular, an abutment 14 which is arranged around the end opening of the cavity 7 and which is configured for abutment coupling against a respective abutment of the element that is able to receive the insert, as will be explained better below. The axial distance between the abutment 14 and each hole 9 will be preset so as to enable the aforesaid coupling by locking pin / s between the insert 1 and the element that is able to receive the coupling.

[0042] The insert 1 may comprise, in particular, at least one reference 15 arranged, in particular, on the stem portion 3 to facilitate the operator who, when assembling the punch, will have to perform correct angular positioning of the insert 1 around the longitudinal axis X with respect to the element to which the insert will be fitted. The reference 15 may comprise, in particular, a visible signal which is arranged externally on the stem portion 3 (for example on a flat surface) in a position that is predefined with respect to the hole / s 9.

[0043] The stem portion 3 may comprise, in particular, a third outer side surface 16 that is arranged between the second outer side surface 6 and the head portion 2. The third outer side surface 16 may have, in particular, a third diameter that is smaller than the second diameter.

[0044] The insert 1 may be used by coupling the insert with a stem 17 by at least one locking pin 10 inserted into a respective hole 9, to form a punch of a moulding unit G for compression moulding doses of material. The assembled punch will thus comprise at least one stem 17 coupled with at least one insert 1 by at least one locking pin 10.

[0045] The second outer side surface 6 of the stem portion 3 of the insert 1 may be axially slidingly coupled with an inner cylindrical surface of the moulding unit G with a movable precision fit with clearance of less than 40 pm, or less than 30 pm, or less than 20 pm.

[0046] The stem 17 may comprise, in particular, an end portion 18 inserted into the axial inner cavity 7 of the stem portion 3 of the insert 1.

[0047] At least one slot 19 mating with the recess 13 formed inside the cavity 7 to define a seat for the locking pin 10 may be, in particular, formed on an outer surface of the end portion 18.

[0048] Each slot 19 could comprise, as in the illustrated embodiments, an incision substantially located in the form of a bevel cut, i.e. a single slot 19 at a respective recess 13, or it is possible to provide a single circumferential groove shared with the various recesses 13.

[0049] The end portion 18 may comprise, in particular, a fourth outer side surface 20 of cylindrical shape. The fourth outer side surface 20 is provided for coupling with the inner side surface 8 of the insert 1

[0050] The stem 17 may comprise, in particular, an abutment 21 abutted against the respective abutment 14 of the insert 1.

[0051] The punch may comprise, in particular, sealing means 22 operating in the cavity 7 between the end portion 18 and the stem portion 3. The sealing means 22 may be, in particular, arranged between a locking pin 10 and the head portion 2. The sealing means 22 may comprise, in particular, an annular gasket.

[0052] As said, the punch may be a component of a moulding unit G, in particular for compression moulding caps made of plastics for closing containers. The moulding unit G comprises an upper half mould 23 with the punch and a lower half mould 24 with the die, in which the punch and the die cooperate together to define a forming cavity in which at least one dose of plastics to be formed is inserted.

[0053] The longitudinal axis X of the insert 1 will have to coincide with a longitudinal axis of the punch that in turn has to be aligned with the compression axis with which the moulding unit G performs the compression action to form an object in the forming cavity. In fact, for correct forming, high precision centering of the punch must be ensured so that the longitudinal axis X of the insert 1 can coincide exactly with the compression axis of the compression moulding unit G.

[0054] In the moulding unit G, there is a free shape coupling with a certain clearance (clearance of the stem portion) between the second outer side surface 6 of the stem portion 3 of the insert 1 and a first cylindrical inner side surface of a punch seat of the moulding unit G (see Figure 8). The second axial length, i.e. the axial length of second outer side surface 6, may be in particular, greater than 2 mm, or greater than 10 mm, or greater than 20 mm, or greater than 40 mm.

[0055] Further, a free shape coupling is provided with a certain clearance (clearance of the head portion) between the first outer side surface 5 of the head portion 2 of the insert 1 and a second cylindrical inner side surface of the punch seat of the moulding unit G (see Figure 8). The first axial length, i.e. the axial length of the first outer side surface 5, may be in particular, greater than 0.3 mm and / or less than 20 mm.

[0056] The clearance of the stem portion may be, in particular, equal to or also less than the clearance of the head portion. The clearance of the head portion may be, in particular, less than 40 pm, or less than 30 pm, or less than 20 pm. The clearance of the head portion may be, in particular, greater than 5 pm.

[0057] The precision of the coaxiality between the punch and the punch seat, and thus the precision of the relative centering of the punch with respect to the compression axis X, is mainly entrusted to the precision of the coupling between the punch seat and the second outer side surface 6 of the stem portion 3 of the insert 1 (in which the second outer side surface 6 may comprise, as in this embodiment, two surface portions that are spaced apart from one another in an axial direction), even if a certain contribution may also be provided by the coupling between the punch seat and the first outer side surface 5 of the head portion 2 of the insert 1.

[0058] The coupling between the punch seat and the first outer side surface 5 of the head portion 2 of the insert 1 can be less precise than the coupling between the punch seat and the second outer side surface 6.

[0059] It is observed that the coupling between the insert 1 and the stem 17, performed by cylindrical (and non-conical) in shape coupling between the inner side surface 8 of the stem portion 3 of the insert 1 and the fourth outer side surface 20 of the end portion 18 of the stem 17, permits precise and reliable coaxiality between the punch and the punch seat, owing to the cylindrical coupling performed with the second outer side surface 6 of the stem portion 3 of the insert 1.

[0060] The stem 17 may have, in particular, a further cylindrical outer side surfacecoupled slidingly with the punch seat of the upper half mould (in an area of free cylindrical coupling with clearance arranged above the area of free cylindrical coupling with clearance of the second outer side surface 6 of the stem portion 3 of the insert 1), that could possibly contribute further to centring of the punch with respect to the compression axis of the mould.

[0061] With reference to Figure 16, the punch may be used in a forming device D configured for compression moulding of plastics, in which the forming device D comprises at least one moulding carousel (in particular with an axis of vertical rotation) in turn comprising a plurality of moulding units G that are angularly spaced apart from one another each of which may be made like the moulding unit disclosed above. Each moulding unit G may be configured, in particular, for forming closures for containers.

[0062] In the embodiment shown in Figure 1, the insert 1 is so made that when the insert 1 is coupled with the stem 17, the front surface 4 of the punch, provided for compression contact with the forming material, belongs entirely to the insert 1. It is possible to provide embodiments (see for example, that of Figure 15) in which only one part of the front surface of the punch in contact with the material belongs to the insert 1, whereas another part belongs to the stem 17, identically, for example, to the punch disclosed in WO 2018 / 015834 Al.

[0063] In these embodiments, the axial inner cavity of the insert 1 is a through cavity and the stem 17, passing through this cavity, arrives as far as to have a central part (for example, circular) of the front surface in compression contact with the material, whereas the insert 1 has a peripheral part (for example, in the form of a circular crown) of this front surface arranged for compression contact with the material (for example the plastics) during the step of compression in the forming cavity, as in the punch disclosed in WO 2018 / 015834 Al.

[0064] In these embodiments (see Figure 15) the punch may comprise, in particular, a separating interface between insert 1 and the stem 17 through which the transit of gas is possible (for example through one or more passages) to enable gas to be extracted from / injected into the forming cavity. The means for the transit of gas may comprise, for example, the same means disclosed in WO 2018 / 015834 Al. It is in particular possible to provide one or more channels inside the head portion of the insert 1 and communicating with the aforesaid means for the transit of gas.

[0065] In all the embodiments disclosed above, the stem 17 and the insert 1 may bemade, in particular, with two at least partially different materials. A material (for example steel) of the stem 17 may be provided, for example, with less heat conductivity than a material (for example a copper alloy or another type of steel) of the insert 1. A material of the stem 17 may be provided, in particular, with mechanical resistance (in particular resistance to wear and / or tensile strength and / or compressive strength) that is greater than a material of the insert 1.

[0066] One embodiment of a work cycle for manufacturing the punch may comprise the following machining steps.

[0067] A first step comprises making the stem 17 and the insert 1 like two separate semifinished workpieces.

[0068] A second step (see Figures 3-7) comprises assembly (by the locking pin / s 10) of the two semifinished workpieces.

[0069] This assembly step may provide, in particular, fixing the stem 17 to a support S and inserting the sealing means 22 into the end portion 18 of the stem 17 (Figure 4). After which, the insert 1 is fixed axially to the end portion 18 until the abutment 14 of the insert 1 comes to about against the abutment 21 of the stem 17 (Figure 5).

[0070] In this configuration each hole 9 and the respective recess 13 in the insert 1 mate with the respective slot 19 on the stem 17, so that it is possible to insert the locking pins 10 (Figure 6). This insertion may be performed with the help of a tool U (Figure 7) This insertion may be performed, in particular, with slightly forced coupling between the pin and the seat thereof.

[0071] A subsequent step is not necessary of further finishing machining of the assembly formed by the two workpieces (insert 1 and stem 17), which are joined together as the concentricity of the assembly formed by the two workpieces is already assured owing to the particular configuration of the insert 1.

[0072] A step of dismantling the two workpieces is possible, by uncoupling the locking pin / s 10 by a tool inside the second opening 12 to push the respective locking pin 10 outside the step thereof.

[0073] Legend:1 insert2 head portion3 stem portion4 front surface5 first outer side surface6 second outer side surface7 cavity8 inner side surface9 holes10 locking pins11 first opening12 second opening13 recess14 abutment of the insert15 reference16 third outer side surface17 stem18 end portion19 slot20 fourth outer side surface21 abutment of the stem22 sealing means23 upper half mould24 lower half mouldX longitudinal axisG moulding unitU toolS supportD forming device

Claims

CLAIMS1. Insert (1) for compression moulding punch, said insert comprising a body extending along a longitudinal axis (X), said body comprising a head portion (2) and a stem portion (3), said head portion (2) comprising a front surface (4) that is transverse to said longitudinal axis (X) and that is configured to contact a material to be moulded, said head portion (2) comprising a first outer side surface (5) that is coaxial with said longitudinal axis (X), said first outer side surface (5) having a first diameter and a first axial length, said stem portion (3) comprising a second outer side surface (6) that is cylindrical in shape and is coaxial with said longitudinal axis (X), said second outer side surface (6) having a second diameter that is less than said first diameter, said stem portion (3) comprising a cavity (7) that has an end opening arranged on a side of said body opposite a side of said front surface (4), said stem portion (3) comprising an inner side surface (8) that is cylindrical in shape and is coaxial with said longitudinal axis (X), said inner side surface (8) having an inner diameter that is smaller than said second diameter, characterized in that at least one hole (9) is obtained on said stem portion (3) and is configured to receive a respective locking pin (10) for coupling said insert (1) with an element that is able to receive said insert, said at least one hole (9) extending between a first opening (11) and a second opening (12) both externally arranged on said stem portion (3), said at least one hole (9) defining a recess (13) which is formed internally on said stem portion (3) and is configured to receive a side portion of a locking pin (10) inserted into said at least one hole (9)2. Insert according to claim 1, wherein said second outer side surface (6) is arranged between said at least one hole (9) and said head portion (2).

3. Insert according to claim 1 or 2, wherein said second axial length is greater than said first axial length, in particular at least twice, or at least three times greater than said first axial length; said first outer side surface (5) comprising, in particular, at least one cylindrical portion whose axial length is less than said first axial length.

4. Insert according to any one of the preceding claims, wherein said first and second openings (11 and 12) are arranged on a lowered area of said stem portion (3) that is recessed with respect to said second outer side surface (6).

5. Insert according to any one of the preceding claims, wherein said inner side surface (8) defines at least partially said cavity (7).

6. Insert according to any one of the preceding claims, wherein said stem portion (3) comprises an abutment (14) which is arranged around said end opening and which is configured for abutment coupling against a respective abutment (21) of the element that is able to receive said insert.

7. Insert according to any one of the preceding claims, comprising at least one reference (15) arranged to promote angular positioning around said longitudinal axis (X) of said insert (1) with respect to the element that is able to receive said insert; said reference (15) comprising, in particular, a visible signal which is arranged externally on said stem portion (3).

8. Insert according to any one of the preceding claims, wherein: a diameter of said first opening (11) is greater than a diameter of said second opening (12), to allow a locking pin (10) to be inserted through said first opening (11), the locking pin (10) to be positioned and to be disengaged by a tool (U) that passes through said second opening (12); and / or said stem portion (3) comprises a third outer side surface (16) that is arranged between said second outer side surface (6) and said head portion (2) and has a third diameter that is smaller than said second diameter; and / or on said stem portion (3) at least one further hole (9) is formed that is configured to receive a respective further locking pin (10), said at least one further hole defining a further recess (13) which is formed internally on said stem portion (3) and is configured to receive a side portion of the further locking pin (10); said further hole (9) comprising a further hole axis that is, in particular, parallel to an axis of said at least one hole (9); and / or said body is made in one piece.

9. Use of an insert (1) according to any one of the preceding claims, wherein said insert (1) is coupled with a stem (17) by at least one locking pin (10) inserted into said at least one hole (9) to form a punch of a moulding unit (G), wherein said second outer side surface (6) is axially slidingly coupled with an inner cylindrical surface of said moulding unit (G) with a precision fit, in particular a movable fit with clearance of less than 40 pm.

10. Punch of a compression moulding unit (G), said punch comprising a stem (17) coupled with an insert (1) by at least one locking pin (10), said insert being made according to any one of claims 1 to 8, said stem (17) comprising an end portion (18)inserted into said cavity (7) of said insert (1), at least one slot (19) being formed on an outer surface of said end portion (18) mating with said recess (13) to define a seat for said at least one locking pin (10), said end portion (18) comprising a fourth outer side surface (20) which is cylindrical in shape coupling with said inner side surface (8) of said insert (1), said insert (1) comprising an abutment (14) abutted against a respective abutment (21) of said stem (17).

11. Punch according to claim 10, comprising sealing means (22) operating between said end portion (18) and said stem portion (3) and arranged between said locking pin (10) and said head portion (2).

12. Compression moulding unit comprising a punch and a die cooperating with each other to define a forming cavity, said punch being made according to claim 10 or 11, a free shape coupling being provided with clearance between said second outer side surface (6) of said stem portion (3) of said insert (1) and a first cylindrical inner side surface of a punch seat of said moulding unit (G); said clearance of said stem portion being, in particular, less than 40 pm.

13. Device for compression moulding of plastics comprising at least one moulding carousel in turn comprising a plurality of moulding units (G), one or more of one or each moulding unit (G) being made according to claim 12; each moulding unit (G) being configured, in particular, for forming closures for containers.

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