Modern sheet metal forming processes used in the automotive industry

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Modern sheet metal forming processes used in the automotive industry

Introduction

Modern continuous rolling mills produce large quantities of thin sheet metal at low cost. A substantial fraction of all metals are produced as thin hot-rolled strip or cold-rolled sheet; this is then formed in secondary processes into automobiles, domestic appliances, building products, aircraft, food and drink cans and a host of other familiar products. Sheet metals parts have the advantage that the material has a high elastic modulus and high yield strength so that the parts produced can be stiff and have a good strength-to-weight ratio.

A large number of techniques are used to make sheet metal parts. This book is concerned mainly with the basic mechanics that underlie all of these methods, rather than with a detailed description of the overall processes, but it is useful at this stage to review brie?y the most common sheet forming techniques.

Steel Panels In Car Body Structure

Ever increasing competition in automotive industry demands productivity improvements and unit cost reduction. The manufacturing engineers and production managers of car body panels are changing their strategy of operation. The days of 'a simple washer to a very complicated fender, all in plant stamping facility', are gone. In-house manufacturing facilities preferably produce only limited number of major car panels.

An automotive plant today produces some 40~50 critical panels per model of car in-house, that require some 100~150 dies. Criteria for taking decision about the panels to be manufactured in-house vary from company to company. Very lately, the stamping plant of the automobile manufacturers includes the types of panels as given below in-house:

External (skin) panels, such as fenders, bonnet, decklid, roof, side panels, doors, etc. Some of these are two panels in a set as left hand and right hand

Internal mating panels, such as bonnet inner, decklid inner or door inner deciding subassembly quality

Dimensionally critical inner panels that are complicated either because of their complex shape or severe draw condition, such as, floor pans, dash panel, etc.

Auto manufacturers prefer to procure the medium and small size panels from vendors depending on the availability (nearer facilities are preferred) and their capability to meet demanded specifications. Some are even farming out the major subassemblies such as doors to specialised vendors. Trends are for farming out as much as possible. The automobile plants are trying to concentrate on assembly operations, leaving specific technology related manufacturing, such as machining and pressing as separate facilities.

Materials For Body Panels

Materials for car body panels require certain specific characteristics to meet the industry's challenges: rationalisation of specifications for leaner inventory, improved formability for reduced rejection rate and better quality. Higher Strength Low Alloy (HSLA) steels of thinner gauges are getting preference for weight reduction and the resulting better fuel economy. Other quality characteristics under demand are higher yield stress (strength), toughness, fatigue strength, improved dent resistance as well as corrosion resistance in materials used for body panels for improved durability and reliability.

To obtain consistent quality of auto body ...