Monthly Archives: April 2021

Lean Bloodletting

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You can find books to support almost any belief

It is easy to caught in the trap of hanging onto outdated beliefs. For this post I happen to choose bloodletting as the example because most people recognize that it has no or very little value. However it was the accepted good practice for over 2000 years. Adding a “lean” label to the practice of bloodletting does not change its usefulness. I also hope that the conspiracy theory people do not pick up on this post and attempt a revival of bloodletting.

Conspiracy theory proponents are not the only ones who can be confused by labels. The lean movement started as a strategy for adding more customers and sales volume in the most cost efficient manner. Within the original MVP (minimum viable product) concept is the word viable. To qualify as being lean, viability is required. Labeling other systems as lean that do not enforce viability can cause pitfalls. They fall into a few categories

a) Company liquidation systems (cost cutting)

b) Quality engineering abdication systems

c) Shortcut scientific method systems using only 4 of 6 steps

From Wikipedia

Bloodletting (or blood-letting) is the withdrawal of blood from a patient to prevent or cure illness and disease. Bloodletting, whether by a physician or by leeches, was based on an ancient system of medicine in which blood and other bodily fluids were regarded as “humours” that had to remain in proper balance to maintain health. It is claimed to have been the most common medical practice performed by surgeons from antiquity until the late 19th century, a span of over 2,000 years.[1] In Europe the practice continued to be relatively common until the end of the 18th century.[2] The practice has now been abandoned by modern-style medicine for all except a few very specific medical conditions.[3] It is conceivable that historically, in the absence of other treatments for hypertension, bloodletting sometimes had a beneficial effect in temporarily reducing blood pressure by reducing blood volume.[4] However, since hypertension is very often asymptomatic and thus not diagnosable without modern methods, this effect was unintentional. In the overwhelming majority of cases, the historical use of bloodletting was harmful to patients.[5]

P20

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The Mini-van used the Common AC Compressor

At the beginning of my HPDC career, the demise of Dohler Jarvis, who invented pressure pins, resulted in the transfer of the dies for the pictured AC front cover to the Chrysler casting plant where I worked. In a panic we not only needed to learn to run these die with pressure pins, but also needed to avoid Dohler pressure pin patent infringement. Many years later I was working with a small air conditioning compressor rebuilder who needed replacement front cover castings. It turned out that mini-vans had a heavy duty cycle that caused the front mount ears to break off of this casting at about 125,000 miles. The normal strategy of buying replacement castings from the original casting supplier was not possible because Chrysler wanted to sell complete replacement air conditioning compressors.

I was also working with a small start-up rheocasting casting plant at that time. The higher ductility 356 semi-solid material was a natural choice to solve the ear breakage problem. The rheocasting process is very effective at making freon tight castings. The only remaining problem was coming up with a casting die at an affordable piece cost. We no longer had the 1,000,000 + annual volume to justify spending $250,000 on a 4 cavity die

Unit Die Body Shared by Many Cavities

Because our total manufacturing volume was estimated to be only 50,000 pieces, we elected to make a single P20 cavity in a unit die. This was copied from the strategy we use for creating dies for prototype castings. The dies for making the original part were cut from the original wood patterns. Thus the part print lacked all of the dimensions needed to CAD create a complete 3D model. We found a complete casting from cavity 31 and used it

to create a 3D CAD model. Since the sample was a machined part we chose and added in machine stock to make a model for the casting. Selected surfaces that were originally machined were made as cast taking advantage of the reduced heat check of the rheocasting process. We omitted the original pressure pin substituting a gate cut off with a cold saw such that the shot biscuit would serve as a pressure pin. Interestingly it was unnecessary to impregnate this casting even though the air conditioning compressor rebuilder already was geared up to impregnate the other castings that he bought and machined.