Custom Shim Manufacturing Via CNC Milling

A metal shim is a thin, flat piece of metal that is often used to fill small gaps between objects. Other purposes where custom shim manufacturing is useful include providing support, ensuring level surfaces, or adjusting tolerances in machinery.

Metal shim manufacturing can be made from titanium, stainless steel, aluminum, copper, or brass. Some of the reasons why metal shims are used across multiple industries include:

• High strength and durability: They are highly resistant to high temperatures and stress compared to plastic, which makes them suitable for heavy-duty applications.
• Save cost in the long run: Metal shim absorbs vibration and wear, thereby protecting complex machinery from damage. This lowers repair costs and downtime.
• Extremely versatile: They are commonly used in the automotive industry for engine component spacing, proper alignment in machinery, structural constructions to level beams, and industrial fixing for mounting machinery to uneven surfaces.

Some of the key considerations when undertaking metal shim manufacturing include selecting the right material depending on application or environmental conditions, precision tolerances to ensure proper alignment, and load requirements. Other factors that will guide the production include the thickness, shape, and flatness.

Anforderungen des Kunden

A client walked into First Mold’s facility to request CNC milling service for custom low volume shim manufacturing. The customer’s preferred material for the creation of this product was titanium. The produced shim was expected to have a standard glossy appearance with a really tight tolerance of ±0.0254mm. The client emphasized strict flatness and thickness tolerance.

“This can be considered a small challenge, especially because of the tight tolerance and the nature of the material,” said First Mold’s General Manager, James Li. “But our focus as a company has always been about putting customer’s needs first.”

Herausforderungen und Lösungen

Although this was a relatively simple-looking product, the material of choice and custom titanium shim – low volume CNC milling presented unique challenges. Titanium is expensive, and scrapping even a single part leads to heavy losses.

Thin titanium alloy parts are particularly difficult to process in CNC machining. Most of our peers are usually unwilling to accept such orders, because titanium alloy is hard to cut, and the thinner the part, the more easily it deforms. Low‑volume production is also uneconomical.

Manufacturing Low Volume Custom Shim

The reason why most suppliers will readily turn down low-volume shim manufacturing is that it is uneconomical. CNC milling of titanium to create a custom shim has high initial fixed costs from machine setup, programming, tool selection, and inspection. This initial fixed cost must be amortized over a small number of parts, leading to a high cost per unit. Other reasons why suppliers turn down low-volume custom shim production include:

• Lack of economies of scale in material purchasing: when manufacturing low volume shim, manufacturers cannot leverage bulk material discounts, leading to a higher cost of raw material.
• Increased labor input: Low-volume productions often require higher manual interventions, custom adjustments, and skilled operator time, which increases the overall cost of production.
• High quality control requirement: Unlike large-scale production, which often benefits from automated processes, smaller-scale productions need rigorous, time-consuming manual inspections.

First Mold has built strong relationships with raw material suppliers, as well as rely on advanced hardware and software capabilities for CNC milling. The combination of these factors helps us to produce low-volume titanium shims that other suppliers dare not accept.

Deformation of Thin Titanium Parts

Not every supplier is skilled at custom shim manufacturing using titanium. This is because of the material’s low elastic modulus or springiness (~110 GPa compared to ~200 GPa of steel). Also, it has poor thermal conductivity (roughly 1/7th that of steel) and high chemical reactivity. These properties can cause significant deflection, residual stress imbalances, or heat-induced distortions during machining.

For example, during machining, the impact of the heat generated at the cutting edge is not carried away by chips, leading to concentrated high temperatures that can exceed 1000°C. The localized heat will cause the thin, weak titanium to expand unevenly during cutting. When it cools, this can lead to warping or significant distortion. Other factors that can lead to deformation when working with titanium include:

• Deformation from clamping: Uneven, radial, or excessive clamping can cause pre-deformation of the shim. Once it is released after machining, the shim will warp or rebound.
• Deformation from “spring back” effect: Every time the machining tool passes during metal shim manufacturing, the thin shim deforms and springs back to the initial position. This can lead to dimensional inaccuracies.
• Work hardening: This happens when the surface layer hardens by 30%. When this happens, it will require increased cutting force, which creates internal stresses.

First Mold has a team of engineers who have worked with titanium for a long time. Together, they created mitigation strategies to overcome some of the challenges of manufacturing a custom shim using CNC milling. Some of the mitigation strategies used by First Mold to meet the client’s requirements include:

• Using soft-jaw clamps: This helps to evenly distribute the pressure to prevent excessive pressure concentration.
• Integrating high-pressure coolant: This helps to manage the heat around the cutting surface, as well as facilitate the removal of chips.
• Using a sharp cutting tool: The sharper the cutting tool, the lower the cutting force. This leads to reduced heat generation and pressure on the shim.
• Stress relief: The team annealed the shim to release internal stresses before finishing. This measure ensured strict flatness and thickness tolerance.

Custom Solutions and Fast Delivery for Prototypes

While most suppliers in China will turn down custom titanium shim – low volume CNC milling, First Mold is capable of fast delivery for low volume projects because of our advanced technology and the partnerships we have built over the years.

For example, in this project, the manufacturer wanted the prototypes delivered in less than four weeks. Sourcing the titanium for the project would have eaten most of the available time. First Mold’s inventory, and those of our partners, include different raw materials. The availability of raw material allowed the team to speed up the manufacturing of custom shim prototypes.

The time saved from sourcing material is invested in perfecting the CAD design of the prototype. First Mold also used the advanced 5-axis CNC machine to reduce setup time by up to 40%, as well as boost precision. The prototype was tested for dimensional accuracy, flatness, and thickness using coordinate measuring machines (CMM) to ensure it meets the customer’s blueprint specification.

Manufacturing Metal Shim for High-End Industries

The client was a high-end manufacturer. The challenge with producing custom shims for high-end industries like aerospace, medical equipment, high-end sports equipment, and precision machinery is that they require extreme attention to material integrity, precision, and manufacturing technique to eliminate defects.

For example, edge burrs must be removed because they can lead to misalignment or create high-friction zones. Some of the critical considerations for high-end custom shim manufacturing include:

• Consistent thickness: The shim must meet extremely tight thickness tolerances to avoid disastrous machine failure. The thickness must be consistent across the entire surface to avoid stress concentrations or uneven loading.
• Surface finish: The surface must have a smooth finish to minimize wear and friction. Since the project involved low-volume manufacturing, First Mold achieved the desired level of surface smoothness and flatness using the lapping technique.

After CNC milling for high-end applications, First Mold cleans and packages the shim to prevent contamination. The reason is that in the aerospace and medical industries, tiny particles can cause failure.

What the Client Gained With First Mold’s Solution

The customer could not hide their excitement when they received the custom shim prototypes ahead of schedule. After inspection, they confirmed that the dimensional tolerance, flatness, thickness, and surface finish were accurate as indicated in the blueprint.

“We are truly grateful to First Mold for accepting to take on this low volume shim manufacturing project,” the client said. “In fact, they were the first of around a dozen suppliers that we contacted that agreed to take on this project. It was a huge relief.”

First Mold did not just ship a few prototypes to the client. We delivered the exact number of custom shims required. By leveraging advanced technology and a dedicated team of engineers with expertise in working with titanium, this project was completed within the client’s budget.

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