Cylinder Cover Plate — Cost Reduction by Process Optimization

CNC MACHINING CASE STUDY

Stainless Steel CNC Machining Optimized for an SS304 Cover Plate

This case study shows how SPM improved stainless steel CNC machining for an SS304 cylinder cover plate by reviewing the complete production route instead of simply accepting an expensive finishing operation. The original process combined CNC turning and milling with double-side grinding to produce the required functional surface.

The challenge was that the SS304 part was non-magnetic, and the double-side grinding process operated at only about three pieces per hour. Grinding alone cost US$4.68 per part, making it the largest single process cost. By replacing this operation with finish turning while retaining the core CNC turning and milling operations, total manufacturing cost fell from US$6.55 to US$2.80 per part — a reduction of 57.3%.

MANUFACTURING CHALLENGE

Why Double-Side Grinding Became the Main Cost Driver

At first glance, this component appears relatively straightforward. CNC turning and milling establish the primary geometry, followed by finishing of the two main surfaces. However, the economics of stainless steel CNC machining are not determined by geometric complexity alone. A seemingly simple finishing requirement can become the dominant cost when the selected process is slow or poorly matched to the material and production volume.

In the original production route, the non-magnetic SS304 component required double-side grinding after the main CNC operations. The grinding process ran at approximately three pieces per hour and added US$4.68 to every component. By comparison, CNC turning cost US$1.09 per part and CNC milling cost US$0.78.

This meant the finishing step cost considerably more than the two core machining processes combined. At a production volume of 500 pieces per month, repeating this low-efficiency operation in stainless steel CNC machining created a substantial recurring cost.

PROCESS OPTIMIZATION

How Stainless Steel CNC Machining Replaced the Grinding Operation

The process review started by looking at the function of the grinding operation rather than treating grinding itself as a mandatory requirement. The engineering question was straightforward: was double-side grinding essential to the component, or was it simply the original method selected to create the required surface?

Once the finishing requirement was considered as part of the complete stainless steel CNC machining route, finish turning became a practical alternative. CNC turning and milling were already required to manufacture the part, so the revised route retained those operations and incorporated the final surface generation into machining instead of sending every component through a separate low-efficiency grinding process.

The result illustrates an important principle in stainless steel CNC machining: process optimization does not always require changing every operation. Sometimes the most effective improvement is to identify one disproportionately expensive step and determine whether its function can be achieved within another process that is already part of the manufacturing route.

SS304 PROCESS CONSIDERATIONS

Why the Complete Machining Route Matters for SS304 Parts

SS304 is an austenitic stainless steel widely used in manufactured components. When planning stainless steel CNC machining, the material specification is only one part of the production decision. The sequence used to generate the geometry and functional surfaces can have an equally important effect on cost, particularly when a separate secondary finishing operation is required.

Austenitic stainless steels also require appropriate machining practices. Technical guidance from the Nickel Institute on machining austenitic chromium-nickel stainless steels provides useful background on machining characteristics and practical considerations for this stainless-steel family.

In this project, the SS304 specification itself was not changed. The optimization instead focused on how the required part was manufactured. This distinction matters because cost reduction should not automatically mean substituting the specified material or compromising a functional requirement. A better stainless steel CNC machining strategy can sometimes be achieved by changing the process sequence while keeping the required material and core component function intact.

COST BREAKDOWN

57.3% Cost Reduction Through Process Optimization

The financial effect of the revised stainless steel CNC machining route becomes significant at repeat-production volume. Eliminating US$4.68 of grinding cost and adding US$0.93 of finish turning produced a net saving of US$3.75 per component.

CNC turning and milling did not become cheaper in the revised stainless steel CNC machining calculation; both remained exactly the same. The saving came from removing the US$4.68 double-side grinding operation and replacing it with US$0.93 of finish turning. This makes the source of the 57.3% reduction clear and avoids attributing the improvement to unrelated machining changes.

WHY THIS APPROACH WORKED

Optimize the Expensive Step, Not Every Step

Manufacturing cost reduction is sometimes approached by asking every supplier to reduce machining prices by a few percentage points. For this component, that strategy would have missed the main opportunity. Turning and milling together represented only US$1.87 of the original US$6.55 unit cost, while double-side grinding alone represented US$4.68.

The larger opportunity was therefore not to negotiate a small reduction in CNC turning or milling. It was to reconsider why the expensive grinding operation existed and whether the same functional objective could be reached differently. Once finish turning was introduced, the grinding operation could be removed from the stainless steel CNC machining process sequence.

Production quantity makes this type of review particularly relevant. A saving of US$3.75 may appear modest when looking at one component. At 500 parts per month, however, it becomes US$1,875 per month. Across 6,000 parts per year, the same process decision produces US$22,500 in annual savings.

DFM FOR REPEAT PRODUCTION

Small Process Changes Can Create Large Annual Savings

This case also shows why DFM should not be limited to the shape of a component. For repeat-production stainless steel CNC machining, manufacturing sequence is part of design-for-manufacturing thinking. A drawing may be fully manufacturable and still leave room for a more efficient production route.

At prototype quantities, suppliers often prioritize flexibility because the cost of developing a specialized process may not be justified. At 500 components per month, the economics change. Every unnecessary minute and every avoidable secondary operation is repeated thousands of times over the life of the project.

That is why SPM evaluates the complete stainless steel CNC machining route when reviewing suitable repeat-production components. The goal is not to remove operations arbitrarily. It is to understand which processes create the required function, which processes create unnecessary recurring cost, and whether the two can be separated.

WHY THIS MATTERS FOR YOUR RFQ

Review Stainless Steel CNC Machining Before Production Is Locked

For an RFQ involving stainless steel CNC machining, SPM looks beyond whether the drawing can simply be produced. Where appropriate, we also review the relationship between material, geometry, machining operations, finishing requirements and production quantity to identify avoidable recurring cost.

This SS304 cover plate is a straightforward example. The core turning and milling operations were not the problem. The cost bottleneck was a slow double-side grinding process added after machining. Replacing that operation with finish turning reduced total cost from US$6.55 to US$2.80 per part while preserving the required functional purpose described for the component.

The same 57.3% saving should not be expected for every project. The value of the example is the engineering approach: identify the actual cost driver first, then evaluate whether the production sequence can achieve the same required function more efficiently.

If you are sourcing a repeat-production stainless steel CNC machining project, you can also review our other manufacturing case studies to see how SPM approaches material utilization, machining strategy, tooling and process optimization across different components.