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A New “Recipe” for MSR Receiver Manufacturing

 

Every component at Detroit Gun Works (DGW) has a defined and proven process, or “recipe.” This concept is derived from our parent company, Central Screw Products (CSP), where we establish recipes for entire global supply chains. Our recipes are distinct to every product we produce and are designed to provide unique value to our customers.

Developing a recipe for a product in the firearms industry posed a challenge. The products don’t change often, and many don’t change at all (the venerable M1911 and AR-15 rifles, for example). The technology evolves, but the OEM product remains largely the same. DGW had to examine its AR-15 Lower Receiver manufacturing process to identify an innovative recipe that could stand out in the industry and maximize customer value.

This journey led back to founding principles behind Detroit Gun Works. DGW was forged in the bottom of the economic recession of 2008, when the commercial heavy truck market had slowed to a crawl and left CSP’s machining equipment idle. We turned our machines on and produced the first DGW Lower Receiver. With this experience in mind, we knew it was critical to build flexibility into our new manufacturing recipe to respond to the fluctuating demands of the market.

Figure 1 – Lang Makro-Grip ViseOur recipe began to take shape. We’ve been proponents of zero-point fixturing for a long time, starting years ago with the Schunk Vero-S, but more recently found a better solution with Lang Technovation. We had been using Lang’s Makro-Grip workholding (Figure 1) for another part recipe on our Makino A51NXs. We knew we wanted to move some of our operations onto the Makinos after seeing the incredible ability of these machines to maintain dimensions in a stable and repeatable fashion.Figure 2 – Makro-Grip Stamping Machine

We had found the Makro-Grip Stamping machine (Figure 2) about a year ago, as an alternative to traditional dovetail workholding. Always determined to reduce costs, we cringed at the fact that we were using a machine tool to put a dovetail on a part, adding excess expense in the process. Dovetailing a workholding surface was not an effective use of our machining time, so the Makro-Grip Stamping combined with the Makro-Grip Workholding provided the robustness and dimensional integrity we needed… without the dovetail expense.

When an OEM customer approached us for sets of their custom upper and lower receivers, we needed a solution for a flexible cell that would allow us to move between DGW contract manufacturing jobs and customer OEM upper/lower configurations. This need led to Lang’s Quick-Point Zero-Point Clamping (Figure 3). The plates allowed us to build repeatable, adaptable tombstones on our horizontal machining centers. We could save our customers money in tooling costs, and the repeatability of the Quick-Point plates (to within 0.0002”) allows for quick change over from job to job. This was looking more and more like our vision for an innovative recipe for our Lower Receiver manufacturing process.
Figure 3- Lang Quick-Point Zero Clamping with Upper Receiver
shown clamped in Makro-Grip Vise

We designed the workholding based around the Quick-Point Plates. This allowed us to take the entire fixture off the machine, with the part in it, and move it to the CMM to get exact measurements to ensure dimensional accuracy. We could then return the fixture to the machine for any subsequent machining operations – with no detrimental impact to finished part accuracy. Our recipe calls for putting all the critical datums in one hold, and between our Makino machining centers, our Quick- Point Zero-Point Clamping workholding, and our engineering creativity, were able to achieve this.

Figure 4- Nikken Trunnion Table inside Brother VMC For a successful recipe, we must supply the most cost effective parts to our customers, so we also make sure to use the right tools for the right job. Once the datums are located on the Makinos, it is time for the parts to move to a less expensive machine. That’s where our Brother machining cell comes in, operated by a Fanuc robot. Our Brother cell is as precise as the Makino’s cell and can reach five sides of the part with our Nikken trunnion tables (Figure 4), but it doesn’t have the horsepower of a Makino. It is the perfect complement to finish the lower receiver.

Figure 5 – Pi Web screen showing dimensional accuracy by
feature along with Cp and CpK values
These changes allowed us to improve our quality to a level beyond what we expected. Our precise and rigid workholding has allowed us to track our quality data like never before. We use a measurement data acquisition system from Zeiss called Pi-Web (Figure 5), part of our overall shop recipe. Pi-Web allows us to gather data and look at trends over time. With this data, we’re able identify small changes and bring dimensions ever closer to the mean, making for a more consistent production process. Additionally, we’re able to collect tool life histories and use Pi- Web as a predictive device that allows us to change out worn tools at a set frequency and avoid broken tools, undersized dimensional features, poor surface finishes, and lost time.

The new recipe has already provided considerable cycle time savings that we look to expand more in the coming months. Our quality improvements yielded great dividends as our scrap rate reduced significantly. The combination of accuracy improvements and flexibility to run lower receivers and other components with our agile and repeatable workholding has become a win-win for DGW and our customers.

Makro-Grip Stamping machineLang’s Quick-Point Zero-Point Clamping
Figure 6- Left image: Raw Forging shown at bottom; finish machined Upper Receiver above. Right image: top view of Lower Receiver before/after machining.

As manufacturing evolves and machines, cutter paths, and tooling choices get more complex, we want to partner with you to turn your machining challenges into the next version of the recipe. DGW is in the business of solving problems and creating solutions that are unique to you and your company. Please contact us for assistance with your outsourced machining projects.