Overcome the Fear of Nickel Superalloys

Challenges and Methods for Machining Advanced Superalloy Materials

The conventional wisdom that nickel superalloys are difficult to machine, whether by cost or failure rate, is rooted in a flawed approach.   Overcoming the difficulties in machining nickel based superalloys is important since they exhibit beneficial characteristics including excellent mechanical strength, resistance to thermal creep deformation, good surface stability resistance to corrosion or oxidation, and their application in extreme, typically high temperature, environments.

Inconel, Hastelloy, Rene, and Waspaloy are nickel superalloy materials utilized as load bearing structures across a number of industries. Example applications include; pressure vessels in petrochemical plants, parts for downhole shafts and wellheads in oil and gas production, biomedical applications and rings, discs and shafts for the hot section of turbine engines. The preeminence of superalloys in aerospace is reflected in the fact that they currently comprise over 50% of the weight of advanced aircraft engines.

Challenges Machining Nickel Superalloys

A flawed approach is that stakeholders including machinists, engineers, designers, process planners, etc. treat these advanced materials like high strength, heat-treated alloys. While similar in physical properties nickel superalloys and heat-treated alloys are fundamentally different at the literal cutting edge. Heat treated materials have a higher tendency to chip and break away under shear forces, like those used by the cutting tools in machining processes. Challenges associated with machining nickel superalloys that all stakeholders should be aware of include;

  • High nickel content leads to work piece hardening.
  • Compressive and shearing forces attack the cutting edge resulting in tool wear and deformation.
  • Frequent tool changing reduces productivity.
  • Removing outer scale from nickel superalloy forgings that are not uniform creates interrupted cuts.
  • Roughly twice as much machine power is needed compared to cutting low-alloy steel.
  • Drilling large diameter deep holes is slow and requires lots of machine power.
  • Material movement, including warpage or dishing, demands machining in multiple operations.

Using nickel superalloys as a manufacturing material requires stakeholders to understand the issues nickel presents. The material does not weaken or deform at higher temperatures, as observed with other types of alloys, therefore nickel is more difficult to deform using typical high precision machining processes. This has kept some from utilizing nickel superalloys even though they may be superior materials depending on the application.

Methods for Machining Nickel Superalloys

Nickel superalloys strength qualities are more uniform with shear, tension, and compression forces resisted. There is no weak point that can be taken advantage of for the cutting process. Simply put, nickel superalloys require higher quality tools that are rigid enough to handle the material. With this in mind, the following tactics can be applied to successfully machine these advanced materials;

  • Consider ceramic tools that are extremely heat resistant.
  • Maintain tool edges to minimize heat buildup, excessive tool wear, and plastic deformation.
  • Optimize cutting speeds to the maximum surface feet per minute (SFPM).
  • Counter work piece flex using rigid setups between tool and work piece.
  • Use the maximum quantity of cutting fluids for heat removal.
  • Operate without coolant to remove forging scale. With the correct grade of ceramic insert this strategy can anneal the material in front of the cutting tool.
  • Optimize a robust, rigid steady rest to support longer nickel superalloy shafts.
  • Rushing nickel superalloys cycle times will result in wasted insert edges and potentially ruined tools.

Approached with the right plan, nickel superalloys can transform the strength profile and heat resistance of a part without incurring excessive costs. Overcoming the stereotypes surrounding these sometimes frustrating materials requires preparation to understand the material specifications, budgeting appropriate job time, and selecting CNC machining service providers with extensive nickel superalloy experience.

Maximizing Machining Relationships – A Conversation with Troy Spies

Following up on a previous post, Maximizing Machining Relationships in Your Supply Chain we talked with Heartland Enterprises Plant Manager, Troy Spies to get a few thoughts on what to look for when selecting a quality CNC machining service provider.

 

Q:  What are the benefits of a good quality management system?

Troy:  It takes a good quality system to have continuous good parts.

Q:  Do the capabilities and quality of a CNC machining service partners machines matter?

Troy:  Good quality machines that are robust and repeatable with a good process you’ll have quality.

Q:  What should you look for when visiting a new shop?

Troy:  Cleanliness is the first thing that you see when they walk in the door.  They see bright lights and clean floors, clean machines, desk tops are clear, instruments are in the right place.  That sets the tone right off the bat for a quality shop.

Heartland Enterprises Overview

Dave Campbell:  We are an ISO certified production machine shop.  Our capabilities focus on 2″ to 42″ diameter parts.   We utilize a wide range of CNC equipment.  We like to use top of the line and we try to stay with Okuma, its very robust equipment.

We built the business with two pillars: taking care of employees and taking care of customers surrounded with the whole element of quality.  Because quality is a mindset and when you want employees you want them thinking quality.   Everybody here cares about the customers and meeting customer needs so that means that as their needs come up we do everything and everybody in the shop does everything they can to meet those needs.

We’re always looking for those things we can do that make us better, faster, quicker.  We have a very rigorous quality process ISO certified of course.   But more important than just the process is the environment in which we have that process working.  We have quality equipment, we have a clean and well organized environment, we have empowered employees, we have teamwork.   All that allows us to deliver quality to the customer.

You know, I often hear people say, “what’s a facility like this doing in Fredericksburg?”