Success in Milling Stainless Steel (a cutting tool test report)
Manufacturers of stainless steel components often face particular challenges when machining specialized parts. Horizon Solutions has expertise when it comes to the cutting tools required to machine these specialized parts. Our team has a focus on improving productivity through innovative cutting tool technology and overall CNC machine tool knowledge.
Stainless Steel Parts: Difficult to Machine
The end user is a manufacturer of finished stainless steel parts used in medical, biomedical and industrial projects. A cutting tool specialist was on-site at the end user account working with a CNC milling machine to determine (1) the existing operation and (2) developing a proposal for a more efficient way to machine the same parts to the same standard.
The material being machined is 316 stainless steel (Ed Note – our blog has previously discussed the overall difficulty of machining 316 stainless steel before with regards to control panel enclosures, here). The machining operation was a milling operation removing material with length of cut approx. 24” and a depth of cut approx. 0.25”. The typical criteria for a tool change was part finish.
The existing operation used an indexable milling cutter. This tool used replaceable inserts, taking four (4) inserts at a time. The programming dictated a cutting speed of 570 SFPM (surface feet per minute) and a spindle speed of 1740 RPM. Using these speeds, the cutter was taking a 0.05” depth of cut. The average cycle time was 13.25 minutes per part. Typically, the 0.05” depth of cut would require 4 or 5 passes to complete. Depending on the initial size and quality of the pre-machined part, an additional pass with a separate tool, also a milling cutter, might be required. This would be determined by a visual inspection by the operator.
Proposal: Increasing Efficiency
Our cutting tool specialist proposed a unique solution. Rather than 4 or 5 passes, and instead of using 2 distinct tools, it was determined that we could complete this machining satisfactorily with one tool and in one pass. The proposed tool was a Pramet indexable milling cutter using a square shoulder milling insert. This tool used replaceable inserts, taking three (3) inserts at a time. The cutting tool specialist actually reduced the cutting speed from 570 to 425 SFPM. Part of the “sweet spot” of this machining was going from 1740 to 1300 RPM. With these speeds and feed, the tool was able to handle a 0.25” depth of cut in one pass. A paraphrased quote from one of the machine operators: “This is impressive.”
The change in programming did result in a significant time reduction, with cycle time going from 13.25 minutes per part to 9.45. The goal is always increased overall productivity. For examples like this, we like to factor in the cost of shop time. This includes the cost of the machine, coolant, electricity, operator, and other shop costs. Depending on materials and machine, your machine cost per hour will typically be between $100 and $150. A specific shop might have different numbers, but these at least give us a number value to put forward for overall productivity. The team at Horizon Solutions has worksheets that factor in additional elements such as the dollar cost per insert, the type of tool holder being used and more.
Cutting Tool Test Report – Milling Stainless Steel
Together, the engineers and operator at the end user worked with the cutting tool specialist to review a variety of numbers to complete a test report. Upon an evaluation we conclude that:
- Assuming a $100/hour machine cost; the proposal will result in a $1850 savings
- Assuming a $150/hour machine cost; the proposal will result in a $2800 savings
These numbers do not factor in the additional savings that may be recouped through not having to utilize a second tool for an additional final pass.
The proposal put forward by Horizon Solutions was implemented on the shop floor. The end user is working with us closely on a future project for additional productivity. For any interested in the actual technology, the insert used was a Pramet Grade M6330 tool. You can learn more about those tools here.
Have you ever done a test report on a machining operation? Do have challenges with machining stainless steel? If so, let us know in the comments section.