Willys Coupe Nose Panel

Copyright © 2002 Dave Propst. All rights reserved.

Revised 4/20/2003

Introduction

This article and the pictures in it illustrate a '40 Willys coupe front grille surround panel (lower portion). This part was made using many normal forming processes such as the English wheel as well as some minor amount of hydraulic press forming. However, the article is not so much a 'how-to' about forming this specific panel as it is about fabrication of such parts in general.

Panel Thickness Issues

Normal preferences are to make replacement parts with metal of the same gauge as the original part. In the case of this Willys part though, 18 gauge steel was used whereas the original was substantially thinner material. This was done because the original part had extensive cracking around all flanges, not only in inside corners as is common on all older cars, but linearly for several inches along the length of some of the grille opening flanges right at the point where the panel breaks over the radius of the flange. This cracking was caused by the OEM part being somewhat overloaded (relative to its thickness) in the sense that it, on it's own, essentially supports and holds in place the great majority of the mass of the grille, hood, both front fenders and inner splash aprons. This same cracking condition in the same location is not altogether uncommon on other examples of the same model of car. The entire OEM panel (of which this replacement part is only a small portion) was, by 1940 standards at any rate, a quite complex, demanding shape to die stamp. In all likelihood this is why it was made of thinner gauge material.

The very car getting this new panel needs new rear fenders as well and those will be made of 18 gauge steel also. The reasoning for this is this car will on occasion see some severe drag race duty and will have an extremely high quality black lacquer paint job. The heavier rear fenders will provide some insurance against damage from being accidentally bumped during wheel/tire changes at the track, debris thrown up during wheelspin, etc.

Building a replacement part with metal heavier than the original part leads to less than well defined flange bend radii because the typical radius is larger simply as a function of the thicker metal. That is, of course, unless special attention is given to forming the flanges to match those of a die stamped, thinner gauge OEM part. This is what has been done in fabricating this grille surround panel so as to end up with a panel that looks original. As a side note-- making a part with metal thicker than OEM is not the only circumstance leading to flanges, corners, and body lines less defined than those found on OEM parts. Many reproduction panels, whether die stamped or custom built, do have this characteristic for any number of reasons.

The pictures below do show it is possible to make flanges and lines that match OEM. Flange radii can be made virtually as sharp as desired; they can in fact be made even sharper than those on this Willys panel. Keep in mind this panel was made to match an existing OEM part even down to the fact that some of the flange radii were tighter than others on the same part.

Additionally, all of the flange corners have been welded to prevent cracks from developing and extending out into the panel surface. Most everyone has probably noticed these types of corners where two flanges come together at 90 degrees (or some similar angle) are frequently the starting point for cracks commonly found in OEM panels. Very few OEM stamped panels found on collector cars of any era have welded or otherwise continuous formed flange corners. Even though welded corners are not true to the original, there is argument for forming continuous flange corners so as to prevent cracks from developing. The exception would be when absolute originality is desired for a particular car.

Surface Finish of Panel

The main surface of this part shows a lack of tooling, grinding, planishing or forming marks, or any kind of irregularities really, even though the main surface of the part has substantial crown. All of the flanges, however, show signs of shrinking, planishing, and forming. It could be assumed that the main surfaces were filed, ground and pneumatic planished to perfection. This is not the case at all though, since, as can be seen, there are few forming marks on the back side. It would be next to impossible to finish and detail out the back side to the level seen here, particularly into the inside corners, if there had been any such marks.

Backing up the explanation for a moment, fabrication of this part was approached from the standpoint of it ultimately being part of a great paint job. For maximum paint appearance and retention of that appearance beyond twelve to eighteen months it is absolutely essential that the metal surface be free of any and all scratches, gouges, tooling blemishes, grinder marks, etc. If any of these are present, eventually they will appear in the paint surface no matter what fillers, sealers or paints are used-- whether catalyzed or not! This is one of the little known but universally true facts of the world of paint. (Catalyzed polyester primer-surfacer of sufficient thickness being the one product that stands a chance of avoiding the inevitable.) So, rather than spending labor time removing such irregularities as well as 0.010, 0.020 or more inches of the metal's thickness by most of the methods mentioned above, it is faster, more effective and less frustrating to simply not allow the irregularities or marks to be put in the panel surface in the first place.

Specifically, all that was done to this panel after the forming was completed was to DA sand the surface with 80 grit and then 120 grit, wire brush the flanges, and finally polish the whole part up with a 3M abrasive pad. The latter was done to 'show up' any blemishes so they could be seen in the pictures. (To very effectively reveal blemishes and marks in a steel panel, DA sand with 120 grit and then polish in one direction with a gray 3M pad.) While the shrinker and forming marks could have been planished, filed or ground out of the flanges, that would be a rather labor intensive task. Additionally in this case, the purpose was to show in these pictures the total degree to which this forming process mars the metal surface. In practice, if there is a case wherein a flange is visible and is a part of the car's paint job, the option of removing any tooling blemishes from that flange always exists.

Panel Construction Issues

No suggestion is made that this panel is an extremely difficult part to build but there is a little more to it than what is immediately apparent. First of all, it is not a custom part of arbitrary dimension. It is a replacement part built to very specific dimension with flanges on all four sides. This means there is no place to 'cheat' on flange corner placement unless the part is made in two or more pieces and welded together. Secondly, the flange on the lower edge is not straight, so it can not be formed on a brake. It is actually concave when viewed head-on so as to appear straight when seen from a normal point of view in front of the car. The flanges on the upper edge (the grille opening) are obviously curved and cannot be brake-formed. The two side flanges are straight so theoretically they could be done on a brake. This would need to be performed before forming the compound curve though, and would be a very awkward, all but impossible way to make the part. So... in order to end up with a panel of correct width and height, all flanges need to be formed by flange tipping method of one kind or another to a very specific spacing and contour after the compound curve is formed. Of course a hammer form or hammer forming buck could have been built to make the part but in this instance only one part is being made. One unit of this part can be built more quickly than the time required to make such a complex hammerform. Also, a wooden hammerform, even of hardwood, likely would not be able to deliver flange corners in 18 gauge as sharp as needed without incorporating metal edges in it's construction.

Metal Shaping Techniques

While the emphasis on not marking up the main surface of a panel is a wonderful goal for someone wanting the ultimate in paint appearance, there is an even more compelling reason for this. The more work done to the main surface of a panel, the more work-hardened it becomes. Stated conversely, the less work done directly on the main surface of the panel, the fewer tooling marks are made and the less work-hardened the panel becomes. This is a win-win situation. The less a panel is work-hardened, the more compliant it is to metalshaping of any kind.

Claims are often made that some of the tools used in sheetmetal work, such as English wheels or power hammers, actually 'undoes' work-hardening of metal in a panel. This is untrue in all non-die-stamp types of forming found in the world of custom panel building. It is not only untrue, the matter is usually stated incorrectly. Such statements equate stress with work-hardening. These are in fact two separate issues. This and other similar misconceptions illustrate the thinking which prevents many from making panels as well as they could. One often hears comments such as "You don't need to know anything of the science of metallurgy to build panels." Or more commonly, "I don't WANT to know anything about what is happening to metal on a microscopic or metallurgical level. I just want to know how to shape panels." If that is someone's mind-set, he will constantly be at the mercy of all the misinformation presented about metal forming. He will not be able to separate fact from fiction and there is far more fiction than fact out there.

Most of the time the subject of work-hardening is discussed in either completely false terms, or, in a vague manner having no influence on methodology. As to the former, plenty of completely false claims are made about how equipment or technique does away with work-hardening or that it completely stress-relieves metal. As to the latter, even in the few cases when work-hardening is referred to in correct terms, it is usually just accepted as one of the realities of metalwork. No regard is given to what influence any true knowledge of it may have on the idea of changing from one method to another to better suit a given task. It is a quite common everyday occurrence that someone, in the process of building a panel, will merrily work away thinking he is un-doing some work-hardening induced by a previous operation --because that is what he has been told-- while in fact he is making the sheetmetal harder and harder (more correctly, stronger and stronger) and therefore progressively more difficult to form and more likely to crack. Particularly with respect to using the English-wheel as a means of planishing out some previously performed mallet work, a common error is to mistake an increase/decrease in rigidity and strength due to the ever-changing mechanical structure of the panel for an increase/decrease in hardness (more correctly-- yield strength) of the material of which the panel is made. This leads to some incorrect assumptions and courses of action. The reality is power hammers, English wheels, pneumatic planishers and all such tools work-harden metal. They do not work-soften metal. They do not reverse the hardening caused by mallet work. They're almost right up there with a shrinker except that they do their work-hardening out in the main body of a panel. Such tools harden metal over a much larger area and with a much more gentle gradient than a shrinker, so the hardening is not so obvious as is the shrinker/stretcher's localized effects on a flange or perimeter.

Any of the false claims about work-hardening and stress-relieving are dramatic examples of what is termed at times in scientific communities as 'fatally flawed' reasoning or theory. Without detailed knowledge of the laws of chemistry or physics, or more specifically in this case metallurgy, it is a relatively common occurrence for people to mistakenly think a statement or test 'proves' something which is in reality utterly false. In other words, if the parameters and statements being used to describe and set up an example, demonstration, test or claim are themselves false, then it should come as no great surprise that the conclusion reached is untrue. A more recent variant of the 'fatally flawed' phrase is the 'garbage in, garbage out' phrase used so often with respect to computer software. It is the same idea.

Certainly work-hardening can never be completely eliminated from the metal shaping process. However, all of what has just been described provides motivation for developing methods that induce less work hardening rather than more work-hardening in the process of achieving a given shape. This always seems to substantially decrease both the labor time and the frustration level. While such methods are neither magic nor quantum leaps forward, they do provide meaningful improvements, particularly with respect to constantly pushing the limits of extreme high-end paint quality.

Does any of this mean certain tools mentioned above are somehow 'no good'? No. Pneumatic planishing hammers, power forming hammers, English wheels, shrinkers and the like are all valid tools. No equipment that can truly shape metal needs any sort of justification beyond the simple fact that the individual wants to own it and/or use it. Meaning, there is little logic in feeling a need to 'prove' that a power hammer can mysteriously build a supposedly better part than an English wheel before one buys a power hammer or vice versa.

Recommended Reading

Upcoming articles will contain some suggested exercises and deductive reasoning that will hopefully allow the reader to confidently verify for himself some of the comments just mentioned. In the meantime, anyone seriously interested in sheet metal work should read two books. The first is Forbes Aird's, The Racer's Encyclopedia of Metals, Fibers and Materials. The second is Carroll Smith's, Engineer to Win. Both books are very well researched. Both authors are very professional and knowledgeable. These books are not misinformed ramblings of self-proclaimed experts. These books present mainstream, verifiable, accepted information in a manner that can be understood by the non-engineer. Both books include references to what the sources are of the information they contain. Neither of these books provides much of any information at all about how to form compound curves in sheetmetal. However, until one has as a foundation the information found in these books, whether it is acquired from these books or some other source, shaping compound curves in sheetmetal will remain, to a degree, somewhat of an unlearned process. Mr. Aird's book is the place to start, as it assumes no previous knowledge or experience. It is a very good introduction to the subject of metal before reading Mr. Smith's book. In Engineer to Win, someplace at about the ninth or tenth chapter, Carroll does wander off into some rather esoteric subject matter mainly of interest to race team personnel, particularly with regards to open-wheel formula car racing. This may or may not be of interest to most people but it has little relevance to the subject of metal. Excluding the later chapters, a person would be wise to read this book several times.

End of Article