Shigeo Shingo was a leading expert in the Toyoda production system as a Japanese industrial engineer. Many current industrial best practices can be traced back to his teaching. This post is on on only one of his teachings. Manufacturing is more cost effective if you utilize processes that do not make chips. This sounds like an impossible command if you are a manufacturer who specializes in machining.

No Shingo was not trying to put all machining suppliers out of business. Some of the processes that machining houses perform can be accomplished chip free. Many chip free processes are the result of a tighter working relationship between the die caster and the machining house

1. Cast chamfers or cast chamfers with counter bores can replace machined chamfers.
2. Form taps can replace cut taps a) Form taps have 5 times the life b) Form taps tolerate some porosity in the bosses c) Structural alloys such as 356 need the work hardening of a form taps to achieve sufficiently strong threads
3. Orbitformed cast studs can replace screwed connections
4. Roll burnishing can solve microporosity in bores
5. Welding is chip free

As die castings get larger we get more concerned about the foot print of the total operation. One of the nice things about chip free operations is that they can be accomplished in final assembly. Moving a part from station to station does not add value. It becomes possible to do less moves if the number of stations is reduced. This means that each station has more operations. Many of my more recent manufacturing cells implement chip tree operations such as form tapping in stations downstream of the CNC machining centers. I have discovered that a tapping head is less expensive per spindle when compared to a CNC machining center spindle

There is no need to 100% inspect the surface hardness of the aluminum casting die inserts. The molten metal will do that for you. Molten metal will highlight the areas that are softer than the expected Rc 44 to Rc 50 range. Aluminum will solder to soft insert surfaces. Due to the physics of heat treatment the insert material at the bottom of the ribs is most likely to be out of specification. Unfortunately cleaning solder out of ribs is very difficult and is almost 100% likely to cause castings to stick in the die. Die casters such as Briggs and Stratton invented laminated dies for their deep fin lawn mower heads to enable creation of proper die insert hardness and draw polish access at the bottom of the fins.

As the die caster, you normally rely on the die shop to confirm the quality of the heat treat. Usually it is too late to fix improper heat treat after the insert is cut to final size. A set of hardness testing files and a visit to the die shop when the inserts are returned from heat treat are even more prudent as a success measure. The reputable die shops will welcome you.

Die Casting would be a lot easier if there were a single trick to making a die run profitably. My experience is opposite to that. It takes a whole bunch of details done near optimum to make a smooth running job. A set of darts on a overflow transfer is just one example. At one shot per minute it is really easy to fill a pit or make a mess over the floor if a overflow wants to break off. Yes, thickening the transfer will keep it attached at the expense of trim break in and die spitting. A better solution is a pair of .7mm thick darts at either end of the transfer, This creates a structural channel cross section that cantilevers the overflow until it is time to trim. For those who don’t believe me, go back to sweeping overflows off the floor.