help me understand these manufacturing processes

[Tall Pine]

Can someone confirm I correctly understand these processes and how they RANK as far as strength of end-product (I am referring to pistol frames & slides). I am real interested to understand what MIM is and why a lot of members don't like it.

1. Milling-take a block of metal and cut/carve it down to the shape you want. Supposed to yield the strongest end-product but is expensive due to the milling process.

2. Forging-heating metal and bending/forming into shape. Maybe also uses pressure and heat together. I don't know how it ranks as far as strength to the ones below.

3. Casting-melting metal and pouring it into a pre-shaped cast. I think it's less strong than the above 2 but not sure, and I have no idea where it ranks with MIM.

4. MIM-metal injection molding. I think this is what it is called. I am really interested in understanding this one. I sense that many feel this is a new process developed to cheaply crank out parts at the expense of the consumer that ends up with a product of inferior quality compared to what it could have been if made with other processes.

Thanks to all who can help me out. TP

 

[mete]

Power metal [PM]parts are made from metal powders compressed in a die then sintered [heated to diffuse atoms and bond particles together] Metal injection molded [MIM] parts are an outgrowth of PM and the metal powder is mixed with a liquid polymer [wax like] and injection molded to form . The parts are then heated to drive off the polymer then further heated to bond the particles......The four basic forming methods each have their benefits and limitations .The choice is made on the basis of the appropriate method for the part.But this is complicated by the choice of steel and the heat treatment of the parts. MIM in the beginning had a learning curve to determine the variables . Apparently they found certain gun parts not suitable for MIM.There is always the problem of QC, that's a full time job for everyone !!! There is some description of PM and MIM on the Remington website .They've been making PM for at least 35 years and I've seen their operation.

 

[Cazach]

Milling is really a finishing operation of forging or casting. It is removing material from either a forged billet or a cast shape.

Forgings are generally the best overall quality and have the smallest chance of defects.

Castings would be second in quality with a higher chance of defects (shrink, gas, sand, etc.)

MIM I do not have any experience with.

 

[Musketeer]

While casting and MIM may seem similar at first there are definite limitations and differences between the two. Generally it is not a matter of one or the other. You may cast larger parts like frames and slides. MIM tends to focus on smaller, more detailed and tighter toleranced parts.

After casting there is often a finishing process (milling, drilling, tapping, etc.). MIM parts tend to have no secondaries.

Forgings are the strongest formed parts. A forging is mechancially deformed into its final shape. Either hot or cold forging results in a part with effectively no voids internally. Both castings and MIM may result in a void, or lack of material in some places. Ideally it is an external defect and easily detected. If it is an internal one it will often only be detected when it fails. This is why the quality level of the shop doing the MIM and Casting is so important. It is also why a casting from one source may be $1.00 and another $3.00, it all comes down to quality.

Although not seen often with firearms there is also fineblanking. This is a cold forging technique like stamping but for thicker walled flat parts. The saw and file blades you see on multi tools are often fine blanked. This would be an excellent proces for thick basically 2-dimensional parts.

Forging/milling is more expensive than MIM which is generally more expensive than Casting.