Method for testing screwing-in performance of self-tapping screw of plastic part

Abstract

The invention provides a method for testing the screwing-in performance of a self-tapping screw of a plastic part. The method comprises the following steps: providing standard values of an insertion torque and a damage torque of screwing the self-tapping screw into the plastic part; providing a testing system for screwing the self-tapping screw into the plastic part; randomly selecting a group of to-be-tested plastic parts and testing one by one; the insertion torque and the damage torque of the self-tapping screw screwed into each plastic part are determined; determining the insertion torque and the damage torque of the self-tapping screws screwed into the group of plastic parts according to the insertion torque and the damage torque of the self-tapping screws screwed into each plastic part; and if the insertion torque of the self-tapping screw screwed into the group of plastic parts is less than or equal to the standard value of the insertion torque and the damage torque of the self-tapping screw screwed into the group of plastic parts is greater than or equal to the standard value of the damage torque, the screwing-in performance test of the self-tapping screw of the plastic parts is qualified. By testing the screwing-in performance of the self-tapping screws of the plastic parts, the situation that unqualified plastic parts enter a production line to affect the production plan of a host can be avoided.

Description

Technical Field

[0001] The present disclosure relates to a performance testing method, and in particular to a method for testing the screwing performance of a self-tapping screw of a plastic part. Background Art

[0002] Currently, self-tapping screws are commonly used to fasten plastic components in the production of home appliances such as gas water heaters and gas wall-mounted boilers. During connection, the prefabricated holes in the screw posts on the plastic components are not pre-threaded. Instead, the self-tapping screws first tap the prefabricated holes to form the internal threads, which are then screwed into the plastic component to secure it. Plastic components are typically provided by suppliers, and OEMs typically only inspect the plastic components for appearance and dimensions during incoming material inspection. If a batch of plastic components fails performance standards, this inspection goes undetected. Consequently, screw threads may strip or the screw posts may crack during assembly, forcing the production line to be shut down for analysis, impacting production schedules. Furthermore, during analysis, OEMs cannot clearly determine whether the problem lies with the plastic component or the self-tapping screws. This leads to the screw and plastic component suppliers shifting blame, shifting the blame to one another, and making quality improvements difficult to resolve. Furthermore, OEMs are forced to replace batches of plastic components, bearing the brunt of the resulting losses. Summary of the Invention

[0003] In order to overcome the problems existing in the related art, the present disclosure provides a method for testing the screwing performance of self-tapping screws of plastic parts to check whether different batches of plastic parts are qualified.

[0004] The present disclosure provides a method for testing the screw-in performance of a self-tapping screw of a plastic part, which includes:

[0005] Provide the standard value of the insertion torque Tis and the standard value of the breaking torque Tos for self-tapping screws screwed into plastic parts;

[0006] A test system for screwing a self-tapping screw into a plastic part is provided. The test system includes a self-tapping screw, a counterpart having a through hole, an electric screwdriver, and a torque tester. The electric screwdriver has a bit, and the torque tester includes a sensor disposed on the bit of the electric screwdriver to collect torque data.

[0007] Randomly select a group of plastic parts to be tested, insert a self-tapping screw through the through hole of the counterpart, and screw it into each plastic part using an electric screwdriver;

[0008] Determine the insertion torque Tin and breaking torque Ton of the self-tapping screw into each plastic part based on the data collected by the torque tester;

[0009] Determine the insertion torque Ti and the breaking torque To of the self-tapping screw screwed into the group of plastic parts based on the insertion torque Tin and the breaking torque Ton of the self-tapping screw screwed into each plastic part;

[0010] If the insertion torque Ti of the self-tapping screw into the group of plastic parts is less than or equal to the standard value of the insertion torque Tis, and the breaking torque To of the self-tapping screw into the group of plastic parts is greater than or equal to the standard value of the breaking torque Tos, the self-tapping screw screwing performance test of the plastic parts is qualified.

[0011] In some embodiments, the step of determining the insertion torque Ti of the self-tapping screw into the group of plastic parts based on the insertion torque Tin of the self-tapping screw into each plastic part includes determining the maximum value of all insertion torques of the self-tapping screw into the group of plastic parts, and determining the maximum value of the insertion torque, or the sum of the maximum value and a predetermined number of standard deviations, as the insertion torque Ti of the self-tapping screw into the group of plastic parts.

[0012] In some embodiments, the step of determining the insertion torque Ti of the self-tapping screw into the group of plastic parts based on the insertion torque Tin of the self-tapping screw into each plastic part includes calculating the average value of all insertion torques of the self-tapping screw into the group of plastic parts, and determining the average value of the insertion torque, or the sum of the average value and a predetermined number of standard deviations as the insertion torque Ti of the self-tapping screw into the group of plastic parts.

[0013] In some embodiments, the step of determining the breaking torque To of the self-tapping screw screwed into the group of plastic parts based on the breaking torque Ton of the self-tapping screw screwed into each plastic part includes determining the minimum value of all breaking torques of the self-tapping screw screwed into the group of plastic parts, and determining the minimum value of the above-mentioned breaking torque, or the difference of the minimum value minus a predetermined number of standard deviations as the breaking torque To of the self-tapping screw screwed into the group of plastic parts.

[0014] In some embodiments, the step of determining the breaking torque To of the self-tapping screw screwed into the group of plastic parts based on the breaking torque Ton of the self-tapping screw screwed into each plastic part includes calculating the average value of all breaking torques of the self-tapping screw screwed into the group of plastic parts, and determining the average value of the above-mentioned breaking torque, or the difference between the average value and a predetermined number of standard deviations as the breaking torque To of the self-tapping screw screwed into the group of plastic parts.

[0015] In some embodiments, the insertion torque is the maximum torque of the self-tapping screw during the tapping stage of screwing into the plastic part, and the breaking torque is the maximum torque of the self-tapping screw during the tightening stage of screwing into the plastic part.

[0016] In some embodiments, the step of determining the insertion torque Tin and the breaking torque Ton of the self-tapping screw screwed into each plastic part based on the data collected by the torque tester includes: drawing a torque curve of the self-tapping screw screwed into each plastic part based on the collected data, determining the value of the highest point of the above torque curve in the tapping stage as the insertion torque Tin of the self-tapping screw screwed into the plastic part, and determining the value of the highest point of the above torque curve in the tightening stage as the breaking torque Ton of the self-tapping screw screwed into the plastic part.

[0017] In some embodiments, the testing method further includes placing the selected group of plastic parts to be tested in an environment of specific temperature and specific humidity for a specific period of time before performing the self-tapping screw screwing test on the selected group of plastic parts to be tested.

[0018] In some embodiments, the step of providing a standard value Tis of the insertion torque and a standard value Tos of the breaking torque for screwing a self-tapping screw into a plastic part comprises:

[0019] Pre-condition the plastic parts by placing them in an environment with a specific temperature and humidity for a specific period of time;

[0020] Screw the self-tapping screw into the pre-treated plastic part and obtain the theoretical values of the insertion torque and the breaking torque;

[0021] The theoretical values of the insertion torque and the breaking torque are corrected according to the actual production environment to obtain the standard values Tis and Tos of the insertion torque and the breaking torque.

[0022] In some embodiments, the specific temperature is within a temperature range of 20 to 25° C., the specific humidity is within a humidity range of 40% to 60%, and the specific duration is within a duration range of 80 to 110 hours.

[0023] The technical solution provided by one or more embodiments of the present disclosure may include the following beneficial effects: by testing the screw-in performance of self-tapping screws of plastic parts, unqualified batches of plastic parts can be screened out before the main unit is assembled, so as to avoid unqualified plastic parts entering the production line and affecting the production plan of the main unit, and it also helps to determine responsibility when quality accidents occur, as well as analyze and solve quality problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present disclosure or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0025] Figure 1This is a connection diagram of a test system for screwing a self-tapping screw into a plastic part disclosed herein during testing in one embodiment;

[0026] Figure 2 yes Figure 1 The diagram shows a torque variation curve of a self-tapping screw during the process of being screwed into a plastic part;

[0027] Figure 3 is through Figure 2 Schematic diagram of torque variation curve obtained by testing a group (ten) of plastic parts randomly selected from a batch using the test system shown;

[0028] Figure 4 It is a flow chart of the steps in an embodiment of a method for testing the screwing performance of self-tapping screws of plastic parts disclosed in the present invention. DETAILED DESCRIPTION

[0029] The following will describe in detail the various embodiments shown in conjunction with the accompanying drawings. However, these embodiments do not represent all embodiments consistent with the present disclosure, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection requested by the appended claims.

[0030] Reference Figure 1 The illustrated system for testing self-tapping screws driven into plastic parts includes a self-tapping screw 31, a countersunk head 32, an electric screwdriver 10, and a torque tester 20. The self-tapping screw 31 includes a head and a shank extending vertically downward from the head. The head can be shaped like a round head, a flat head, a pan head, a countersunk head, a countersunk head, a cylindrical head, a trumpet head, a hexagonal head, or the like. The shank has threads formed on its circumferential outer surface, and its distal end can be flat or pointed. The countersunk head 32 is a component adjacent to or connected to the target part (e.g., the plastic part to be tested) during assembly and can be either metal or plastic. The countersunk head 32 is provided with a through hole for the shank of the self-tapping screw 31 to pass through. The electric screwdriver 10 can be an Atlas EBL series, such as the EBL55, which has a bit 11. The torque tester can be a Desoutter DELTA 6D, which includes a sensor 21 mounted on the electric screwdriver bit 11 to collect torque data. In addition, the plastic part 40 to be tested generally has a screw column with a prefabricated hole provided therein.

[0031] Figure 2The torque curve of a self-tapping screw as it is screwed into a plastic part is detailed. During the tapping phase, when the screw is creating threads in a prefabricated hole in the plastic part, it initially has a low torque, T1. As the screw penetrates deeper, the torque gradually increases, as shown in T2. When the screw has fully formed its threads in the prefabricated hole, it reaches its maximum torque, known as the insertion torque, Ti. As the screw is further inserted, it enters the tightening phase, where the torque continues to increase, and the curve rises. At a certain value, the screw locks onto the workpiece and the plastic part. This torque is known as the tightening torque, TL. As torque is applied to the screw and tightened further, the torque continues to rise. After reaching its maximum value, the screw may fail due to thread stripping or cracking of the screw stud in the plastic part. The torque then decreases. The maximum torque during the tightening phase of the self-tapping screw's screwing into the plastic part is known as the breaking torque, To. In practice, the breaking torque, TL, is typically determined by measuring the insertion torque, Ti, and the breaking torque, To. This value, such as the midpoint between the insertion torque, Ti, and the breaking torque, To, is then used as the torque setting for the electric screwdriver used by workers on the production line.

[0032] Reference Figure 4The method for testing the screw-in performance of self-tapping screws in plastic parts according to one embodiment of the present disclosure is shown. First, a standard value Tis for the insertion torque and a standard value Tos for the breaking torque of a self-tapping screw in a plastic part are provided (step 501). These standard values are obtained by the host manufacturer through testing using standard self-tapping screws, handpieces, and plastic parts. Due to the diverse molding processes of plastic parts, the same raw materials are affected by different environmental conditions and have different shrinkage rates, resulting in significant performance differences. In some embodiments, the standard plastic parts can be placed in an environment with a specific temperature and humidity for a specific period of time for preconditioning. The specific temperature is within the temperature range of 20-25°C, preferably within the temperature range of 22-24°C, such as 23°C; the specific humidity is within the humidity range of 40%-60%, preferably within the humidity range of 45%-55%, such as 55%; and the specific duration is within the duration range of 80-110 hours, preferably within the duration range of 88-100 hours, such as 95 hours. The self-tapping screw is then screwed into the pre-treated plastic part, and the theoretical values of the insertion torque and the breaking torque are obtained. For example, the theoretical value of the insertion torque is 0.25 Nm, and the theoretical value of the breaking torque is 0.52 Nm. In some embodiments, the theoretical values of the insertion torque and the breaking torque can be used as the standard values of the insertion torque and the breaking torque Tis and Tos. Since the pre-treatment conditions are relatively harsh and time-consuming, in other embodiments, the theoretical values of the insertion torque and the breaking torque can be corrected according to the actual production environment of the supplier to obtain the standard values of the insertion torque and the breaking torque Tis and Tos. For example, by conducting multiple tests in the actual production environment of the supplier and comparing them with the tests under the theoretical environment conditions, the theoretical value of the insertion torque of 0.25 Nm can be corrected to 0.3 Nm, which corresponds to the standard value of the insertion torque Tis of this supplier, and the theoretical value of the breaking torque of 0.52 Nm can be corrected to 0.45 Nm, which corresponds to the standard value of the breaking torque Tos of this supplier.

[0033] A test system for screwing self-tapping screws into plastic parts as described above is provided (step 502), including a standard self-tapping screw 31 and a counterpart 32, as well as an electric screwdriver 10 and a torque tester 20. When the supplier produces a batch of plastic parts, a group of plastic parts are randomly selected and tested one by one (step 503). In some embodiments, the plastic parts to be tested can be placed in an environment of specific temperature and specific humidity for a specific period of time before testing for pretreatment. The standard values of insertion torque and destructive torque corresponding to the pretreated plastic parts to be tested are Tis and Tos, which are the theoretical values of the above-mentioned insertion torque and destructive torque. In addition, the specific temperature, specific humidity, and specific duration are the same as those in the above embodiment, and the applicant will not elaborate on them here. This testing work can be completed during the incoming material inspection of the host manufacturer, or it can be completed before the supplier leaves the factory. In some embodiments, the self-tapping screws 31 are passed through the through holes of the counterpart 32 one by one and screwed into the screw posts of each plastic part 40 using the electric screwdriver 10. Then, the insertion torque Tin and the breaking torque Ton of the self-tapping screws screwed into each plastic part are determined based on the data collected by the torque tester 20 (step 504). Figure 3 In a specific example shown, a torque curve of a self-tapping screw being screwed into each plastic part can be drawn based on the data collected by the torque tester 20. For example, there are ten plastic parts randomly selected in this example, and ten torque curves can be obtained; then, the value of the highest point of each torque curve in the tapping stage is determined as the insertion torque Tin of the self-tapping screw being screwed into the plastic part, and the value of the highest point of each torque curve in the tightening stage is determined as the breaking torque Ton of the self-tapping screw being screwed into the plastic part.

[0034] Subsequently, the insertion torque Ti and the breaking torque To of the self-tapping screw into the group of plastic parts are determined based on the insertion torque Tin and the breaking torque Ton of the self-tapping screw into each plastic part (step 505). Regarding the determination of the insertion torque Ti of the self-tapping screw into the group of plastic parts, in some embodiments, the maximum value of all insertion torques of the self-tapping screw into the group of plastic parts is first determined, and then the maximum value of the insertion torque, or the sum of the maximum value and a predetermined number of standard deviations, is determined as the insertion torque Ti of the self-tapping screw into the group of plastic parts. In other embodiments, the average value of all insertion torques of the self-tapping screw into the group of plastic parts is first calculated, and then the average value of the insertion torque, or the sum of the average value and a predetermined number of standard deviations, is determined as the insertion torque Ti of the self-tapping screw into the group of plastic parts. Regarding the determination of the breaking torque To of the self-tapping screw when screwed into the group of plastic parts, in some embodiments, the minimum value of all the breaking torques of the self-tapping screw when screwed into the group of plastic parts is first determined, and then the minimum value of the breaking torque, or the difference of the minimum value minus a predetermined number of standard deviations, is determined as the breaking torque To of the self-tapping screw when screwed into the group of plastic parts; in other embodiments, the average value of all the breaking torques of the self-tapping screw when screwed into the group of plastic parts is first calculated, and then the average value of the breaking torque, or the difference of the average value minus a predetermined number of standard deviations, is determined as the breaking torque To of the self-tapping screw when screwed into the group of plastic parts. Figure 3 In the example shown, the insertion torque Ti of the self-tapping screw into the group of plastic parts is the average of the insertion torques of the self-tapping screw into the ten selected plastic parts plus the sum of three standard deviations. The failure torque To of the self-tapping screw into the group of plastic parts is the average of the failure torques of the self-tapping screw into the ten selected plastic parts minus three standard deviations. The standard deviation is the square root of the arithmetic mean (i.e., variance) of the squared deviations from the mean, usually denoted by σ, and its formula is:

[0035]

[0036] Where n is the total amount of data, such as n = 10 in this example;

[0037] Xi is the set of values, such as ten insertion torques or ten breaking torques in this example;

[0038] μ is the average value of the group of values, such as the average value of ten insertion torques or the average value of ten breaking torques in this example.

[0039] Determine whether the insertion torque Ti of the self-tapping screw screwed into the group of plastic parts is less than or equal to the standard value Tis of the insertion torque, and whether the breaking torque To of the self-tapping screw screwed into the group of plastic parts is greater than or equal to the standard value Tos of the breaking torque (step 506); if so, it indicates that the performance test of the batch of plastic parts is qualified (step 507), because the locking torque TL between the standard value Tis of the insertion torque and the standard value Tos of the breaking torque must also fall within the range between the insertion torque Ti and the breaking torque To of the self-tapping screw screwed into the group of plastic parts; otherwise, it indicates that the performance test of the batch of plastic parts is unqualified (step 508), because the above-mentioned locking torque TL may fall outside the range between the insertion torque Ti and the breaking torque To of the self-tapping screw screwed into the group of plastic parts.

[0040] By testing the screw-in performance of self-tapping screws on plastic parts, unqualified batches of plastic parts can be screened out before the main machine is assembled, so as to prevent unqualified plastic parts from entering the production line and affecting the production plan of the main machine. It also helps to determine responsibility when quality accidents occur, as well as analyze and solve quality problems.

[0041] In the description of the above embodiments in the present disclosure, the orientations or positional relationships indicated by “longitudinal”, “transverse”, “vertical”, “radial”, “circumferential”, “horizontal”, “length”, “width”, “thickness”, “up”, “down”, “left”, “right”, “front”, and “back”, etc., are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience and simplification of the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present disclosure.

[0042] In the above disclosure, the terms "first," "second," and the like are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features being referred to. Thus, a definition of a feature such as "first," "second," and the like may explicitly or implicitly include at least one such feature. In the above description, "several," "a plurality," and similar terms mean at least two, such as two or three, unless otherwise specifically defined.

[0043] In the above disclosure, unless otherwise expressly specified or limited, terms such as "mounted," "adjacent," "connected," "connected," and "fixed" should be interpreted broadly. For example, they may refer to fixed connections, detachable connections, or integration; they may refer to direct connections or indirect connections through an intermediate medium; they may refer to internal communication between two elements or interaction between two elements, unless otherwise expressly limited. Those skilled in the art will understand the specific meanings of these terms in this disclosure based on specific circumstances.

[0044] It should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for testing the screw-in performance of self-tapping screws for plastic parts, characterized by: The method includes Provide the standard value of the insertion torque (Tis) and the standard value of the breaking torque (Tos) for self-tapping screws screwed into plastic parts; A test system for screwing a self-tapping screw into a plastic part is provided. The test system includes a self-tapping screw, a counterpart having a through hole, an electric screwdriver, and a torque tester. The electric screwdriver has a bit, and the torque tester includes a sensor disposed on the bit of the electric screwdriver to collect torque data. Randomly select a group of plastic parts to be tested, insert a self-tapping screw through the through hole of the counterpart, and screw it into each plastic part using an electric screwdriver; The insertion torque (Tin) and breaking torque (Ton) of the self-tapping screw into each plastic part are determined based on the data collected by the torque tester; Determining the insertion torque (Ti) and the breaking torque (To) of the self-tapping screw screwed into the group of plastic parts according to the insertion torque (Tin) and the breaking torque (Ton) of the self-tapping screw screwed into each plastic part; If the insertion torque (Ti) of the self-tapping screw into the group of plastic parts is less than or equal to the standard value of the insertion torque (Tis), and the breaking torque (To) of the self-tapping screw into the group of plastic parts is greater than or equal to the standard value of the breaking torque (Tos), the self-tapping screw screwing performance test of the plastic parts is qualified.

2. The testing method according to claim 1, wherein: The step of determining the insertion torque (Ti) of the self-tapping screw into the group of plastic parts based on the insertion torque (Tin) of the self-tapping screw into each plastic part includes determining the maximum value of all insertion torques of the self-tapping screw into the group of plastic parts, and determining the maximum value of the insertion torque or the sum of the maximum value and a predetermined number of standard deviations as the insertion torque (Ti) of the self-tapping screw into the group of plastic parts.

3. The testing method according to claim 1, wherein: The step of determining the insertion torque (Ti) of the self-tapping screw into the group of plastic parts based on the insertion torque (Tin) of the self-tapping screw into each plastic part includes calculating the average value of all insertion torques of the self-tapping screw into the group of plastic parts, and determining the average value of the insertion torque, or the sum of the average value and a predetermined number of standard deviations, as the insertion torque (Ti) of the self-tapping screw into the group of plastic parts.

4. The testing method according to claim 2 or 3, characterized in that: The step of determining the breaking torque (To) of the self-tapping screw screwed into the group of plastic parts based on the breaking torque (Ton) of the self-tapping screw screwed into each plastic part includes determining the minimum value of all breaking torques of the self-tapping screw screwed into the group of plastic parts, and determining the minimum value of the breaking torque, or the difference obtained by subtracting a predetermined number of standard deviations from the minimum value, as the breaking torque (To) of the self-tapping screw screwed into the group of plastic parts.

5. The testing method according to claim 2 or 3, characterized in that: The step of determining the breaking torque (To) of the self-tapping screw screwed into the group of plastic parts based on the breaking torque (Ton) of the self-tapping screw screwed into each plastic part includes calculating the average value of all breaking torques of the self-tapping screw screwed into the group of plastic parts, and determining the average value of the breaking torque, or the difference obtained by subtracting a predetermined number of standard deviations from the average value, as the breaking torque (To) of the self-tapping screw screwed into the group of plastic parts.

6. The testing method according to claim 1, wherein: The insertion torque is the maximum torque of the self-tapping screw during the tapping stage when screwing into the plastic part, and the breaking torque is the maximum torque of the self-tapping screw during the tightening stage when screwing into the plastic part.

7. The testing method according to claim 1 or 6, characterized in that: The step of determining the insertion torque (Tin) and the breaking torque (Ton) of the self-tapping screw screwed into each plastic part based on the data collected by the torque tester includes: drawing a torque curve of the self-tapping screw screwed into each plastic part based on the collected data, determining the value of the highest point of the torque curve in the tapping stage as the insertion torque (Tin) of the self-tapping screw screwed into the plastic part, and determining the value of the highest point of the torque curve in the tightening stage as the breaking torque (Ton) of the self-tapping screw screwed into the plastic part.

8. The testing method according to claim 1, wherein: The method further includes placing the selected group of plastic parts to be tested in an environment of specific temperature and specific humidity for a specific period of time before performing the self-tapping screw screwing test on the selected group of plastic parts to be tested.

9. The testing method according to claim 1, wherein: The step of providing a standard value of the insertion torque (Tis) and the standard value of the breaking torque (Tos) of the self-tapping screw screwed into the plastic part comprises: Pre-condition the plastic parts by placing them in an environment with a specific temperature and humidity for a specific period of time; Screwing a self-tapping screw into the pre-treated plastic part, and obtaining theoretical values of insertion torque and breaking torque; The theoretical values of the insertion torque and the breaking torque are corrected according to the actual production environment to obtain the standard values (Tis, Tos) of the insertion torque and the breaking torque.

10. The testing method according to claim 8 or 9, characterized in that: The specific temperature is within a temperature range of 20 to 25° C., the specific humidity is within a humidity range of 40% to 60%, and the specific duration is within a duration range of 80 to 110 hours.

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