Variable-Thickness Impact Extrusion for Pressure-Resistant Container Rims
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Solution Overview
Problem
Conventional impact extruded preforms with constant tubular wall thickness face challenges during expansion shaping, particularly in pressure ram forming, due to uneven material thickness leading to stress concentrations and potential container failure at the rim section under internal pressure.
Innovation Solution
A method and tooling for impact extruding preforms with variable sidewall thickness, including a transition wall thickness that is larger than the sidewall thickness, to create a strengthened rolled-in rim section during the pressure ram forming process, enhancing the container's pressure resistance and preventing unrolling of the rim.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional impact extrusion produces preforms with constant tubular wall thickness, then the manufacturing process is simple and efficient, but the preforms exhibit stress concentrations and potential container failure at the rim section under internal pressure
Solution Approach 1:
The punch tooling incorporates a land portion with specific dimensions (axial width and radial distance from axis) that creates a transition wall region in the preform with increased wall thickness. This local quality change concentrates material where needed (at the rim section) to withstand internal pressure, while the rest of the preform maintains optimal thickness for other functions.
2Reliability
If the tubular wall thickness is increased to prevent container failure, then pressure resistance improves, but material usage increases and manufacturing cost rises
Solution Approach 1:
Instead of uniformly increasing wall thickness throughout the preform, the invention applies increased thickness locally only at the rim section through the land portion of the punch. This ensures pressure resistance where needed while minimizing overall material consumption.
Solution Approach 2:
The variable wall thickness is created during the initial impact extrusion process itself, rather than requiring subsequent thickening operations. The land portion on the punch pre-forms the transition wall region with increased thickness, eliminating the need for additional material or processing steps.
3Quantity of substance
If the tubular wall thickness is decreased to use thinner materials, then material cost reduces, but the rim section becomes weaker and more prone to failure under pressure
Solution Approach 1:
The invention allows the use of thinner materials for the majority of the preform while compensating for rim section weakness by creating a localized thickened transition wall region. This enables overall material reduction while maintaining or improving pressure resistance at the critical rim section.
4Ease of manufacture
If the wall thickness is made uniform throughout the preform, then manufacturing is simpler, but the change in direction and thickness at the juncture of the closed end with the sidewall creates stress concentrations
Solution Approach 1:
The land portion on the punch creates a localized transition wall region with increased thickness specifically at the juncture of the closed end with the sidewall. This local modification eliminates stress concentrations at this critical junction without complicating the overall manufacturing process, as the variable thickness is inherently created during impact extrusion.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The preforms with variable thickness exhibit improved pressure resistance and reduced risk of container failure, allowing for the use of thinner materials and maintaining container shape integrity under elevated internal pressures.
Implementation Method 1
impacting a metal billet to plasticize the metal and redirect the plasticized metal
Implementation Method 2
a hollow metal preform is placed in a die cavity... Upon being subjected to internal fluid pressure, the preform expands outwardly into substantially full contact with the die wall
Data Source
AI summary
A hollow preform impact extruded from a metal billet to produce a progressing wall at a transition wall thickness. An axially forward portion of the progressing wall is ironed by extrusion past an extrusion point to form a sidewall portion of a lesser thickness. Extruding is stopped while some of the billet remains to form the closed bottom end. The preform has a bottom portion, a sidewall portion and a transition wall portion extending between the bottom portion and the sidewall portion. The transition wall portion is thicker than the sidewall portion and can be formed into at least part of the rim of an expansion shaped container. An impact extrusion punch has a central axis, an axially forward, impact surface for impacting metal to be extruded, a transition region for directing material displaced by the impact surface and a rear extrusion point for ironing material extruded past the transition region.