Die casting machining is the critical process that bridges the gap between a raw metal part and a high-precision industrial component. In this session, we are taking you through the steps of die casting machining for simple castings and, in particular, how to get the angles between the faces spot on. This article explores manufacturing technology where we dive into the practical side of die casting machining and how it applies to real-world production.
To produce high-quality parts through die casting machining, you need a pattern. This is the starting point for the entire process. These patterns might be made of wood by skilled old-time pattern makers, or these days, patterns are just as likely to be 3D printed for rapid prototyping to streamline the die casting machining workflow.
The Science of Pattern Making and Shrinkage
What the pattern makers would do is allow for a certain amount of shrinkage you get on a casting. If you’ve got non-uniform sections, they are going to cool quicker and might distort. Really skilled pattern makers could anticipate that in their head.
The pattern you’ve got may not look exactly like the finished part; it might have a bit of a curve to it, designed so that once it comes out of the mold and does all its cooling, it pulls into the finished shape the design called for. This guide explores the secrets of the trade, explaining why die casting machining is a major leap over traditional methods.
What are Machined Castings?
In its simplest terms, machined castings are the result of a manufacturing process where molten metal is introduced into a mold and then refined with precision cutting tools. As the process unfolds, the metal comes in, the part is formed, and then it is processed down the line through various die casting machining stages. However, a casting will come out of the sand with “draft” on it, a slight taper, and usually a little bit over-size with a few radii.
Draft is purely so the pattern can come out of the mold. Typically you have three degrees or something like that, which means trying to clamp on that is going to be difficult. That is the first big clue on setting up castings: you need a parallel side if the designer has their thinking caps on. If not, the machinist has to create one through die casting machining.
Usually, the skin of these things is pretty tough; it’s got sand mixed in with it, it’s cooled the fastest, and it’s approaching white iron. This is why specialized casting machining is required to reach final specifications. According to the North American Die Casting Association, secondary machining is required for approximately 50% of all die-cast parts to meet functional tolerances.
The Role of Die Casting Machining
When we talk about die casting machining, we are looking at taking that raw, rough shape and turning it into something functional. Typically, the foundry will dress it up a little bit, but basically, it’s up to you as the machinist to do your thing. You need to clean up the faces to get a decent surface that you can use as a basis for your clamping. Whether you’re working on a fixture block or a complex gearbox housing, the goal is to get that first datum face flat so everything else can follow.
Managing Casting Machining Tolerance
When a new customer comes to us, we look at tolerances, part size, and various features to pinpoint the right alloy. Getting a tight casting machining tolerance is often a battle against the internal stresses of the metal. Because of the casting process, when the metal cools, the skin does first of all and then the inside does.
Stress Relief and Equalization
If you can imagine the molten metal on the inside contracting, it’s going to try to be pulling the skin. There’s a story about a certain luxury car maker who used to cast their engine blocks and then put them out the back in a paddock for a decade or so just to let the stresses equalize. There are modern processes to stress relief castings as well, but in the shop, we handle this by taking a minimum clean-up on all faces during die casting machining.
If you spend all this time getting one face beautifully flat and smooth and then you do the next face, the part might twist a little bit on you because you removed material here and haven’t removed material there. By doing a roughing pass on all three faces and then coming back once the casting has had a chance to “work out where it is,” you can maintain a much better casting machining tolerance. This is vital for high-precision trykkstøping av aluminium prosjekter.
Factors Influencing Casting Machining Cost
If you want to keep your casting machining cost down, you have to be smart about how much material you are removing. The design of the casting should allow three millimeters (an eighth of an inch) or something like that on there to be machined off if you want a good machining surface.
| Challenge | Impact on Casting Machining Cost | Løsning |
| Utkast til vinkler | High (difficult clamping) | Design parallel clamping webs into the pattern. |
| Hard Spots | High (tool breakage) | Use carbide cutters and lower surface speeds. |
| Porosity/Voids | Very High (scrapped parts) | Use vacuum die casting to ensure density. |
| Setup Time | Medium | Use angle plates and levels to find datums quickly. |
Grey cast iron, in particular, is rather messy stuff. You should have your vacuum cleaner over the place to take up chips to prevent machinery wear. At diecastingschina.com, we help customers minimize casting machining cost by optimizing the “as-cast” geometry to reduce the number of CNC setups required for die casting machining.
Die Casting Machining for Replacement and Repair
Sometimes we have a broken casting, maybe an accidental breakage at work where a chunk broke off. In these cases, we might have to use a sample of an identical part to get a really good hole pattern. When you’re drilling these machined castings, you have to be prepared for the unexpected. You might run into a hard spot that starts to dull your new drill bit.
If you hit a hard spot on the face, you might need to use a carbide straight flute drill. It definitely wasn’t expected, but carbide will cut through where high-speed steel just chatters. If the casting is so hard that it’s destroying drills, it might have been pulled from the mold too fast. Generally, these kind of castings need to set and soak in the mold for about 24 hours so they don’t get hard on the outside. If they do get hard, they may need to be annealed.
The Braze Repair Method
If a casting breaks during drilling because of a thin wall and high pressure, you might attempt to save it by braising it back up. You build the metal up, wrap it in a fiberglass blanket with insulating tiles, and let it sit overnight to cool down slowly. This slow cool-down helps anneal the part, making it easier to machine the face later. At diecastingschina.com, we aim to get the “most bang for the buck” by avoiding these failures through proper thermal management during the initial cast.
Technical Setups: The Machinist’s Tricks
The main trick to machining off faces on machined castings is getting the part level. The bed of a machine isn’t always precisely flat, so you might use an adjustable level to set things up.
- Datum Faces: Choose one face, maybe the one with the thinnest wall, to be your datum. Clean it up so you have a decent surface for clamping.
- Angle Plate Setup: Mount a carbide face cutter and use an angle plate to tie everything in. If the part is twisting as the cutter hits, you may need to add a second angle plate.
- Surface Speed: Bear in mind that the recommended surface speed for grey cast iron is about half that of steel, so adjust your speeds down accordingly.
- Spalling: Cast iron is strong in compression and weak in tension. When running your cutter, run it into the work. If you run it out of the work, you’ll tend to get it chipping and spalling on the edge.
Achieving Parallelism and Matching Angles
Once you have one block machined and one not, you might find a mismatch in the angles. To get them to match up, you take the one you’re calling “good” and put it on top of the other. You might have to jack the back corner up with shims so you don’t take too much off, but because the angles are equal, the surfaces become parallel.
If you want to be really pedantic about this and get better accuracy than a standard protractor, you could put a sine block on there and run an indicator along. Use shims to lift it ever so slightly until you get it flat. Then you know that angle is exactly whatever the design called for with respect to the mill travel. This level of precision is how we guarantee a high casting machining tolerance for industrial fixtures.
Sourcing Machined Castings from China
For global manufacturers, sourcing from trykkstøping av aluminium experts in China provides a significant advantage. Modern facilities utilize AI-driven vacuum die casting to ensure the internal “meat” of the metal is solid. This is essential for die casting machining because machining into a gas pocket or “void” can result in a scrapped part.
Modern die casting machining in China utilizes specialized carbide face cutters. Bear in mind the recommended surface speed for grey cast iron is about half that of steel; so adjust your speeds down accordingly for your die casting machining operations. At diecastingschina.com, we provide the technical experience needed to navigate these complex setups and help you get the “most bang for your buck” out of every die casting machining project.
Value-Added Processes and Quality Assurance
Beyond the initial cut, casting machining involves many steps:
- In-house CNC Machining: From simple drill/tap stations to complex 5-axis work.
- Leak Testing: We inject the part with air and measure the decay to confirm a leak-free product.
- Overflatebehandlinger: From vibratory deburring to high-level corrosion protection.
We use custom gauging and x-ray of parts to ensure there are no micro-voids. If a part has tiny holes, we can perform resin impregnation, which helps fill any voids to meet the leak-free requirement. Our objective is to facilitate the design so the final product is both durable and cost-effective.
Why Partner for Machined Castings?
In this session, we discussed how patterns are made, why draft matters, and how to master die casting machining for simple and complex castings. We love working with these parts and talking to customers about their new die casting machining applications. If a part isn’t a good fit for die casting machining, we will help you find the right manufacturing process that fits your part.
At The Die Casting, we provide the technical experience needed for the ever-increasing amount of electronics and mechanical parts in the world today. Whether you need an intricate structural part or high-volume die casting machining, we will give you an honest opinion and help you get the part to an ideal solution.
