Understanding the 5 Physical Properties of Workpiece Materials

By Tim Aydt, Product Manager – Milling

Whether you are machining parts from cast irons, low-alloy steels or nickel-based alloys, all such materials exhibit five basic physical properties in varying levels. Those properties are abrasiveness, hardness, thermal conductivity, tendencies toward adhesion/ductility and strain hardening.

The proportions of the individual properties in a given workpiece material largely determine its machinability. Relatively soft low-alloy steel will exhibit strong tendencies to adhesion that can lead to edge buildup on a cutting tool and diffusion wear. On the other hand, poor thermal conductivity of a tough nickel-base alloy can generate extreme cutting temperatures that will cause a tool to deform and fail.

In theory, a material’s specified mix of alloying elements determines the type of cutting tools and cutting parameters that will, in turn, produce predictable and normal wear patterns and help increase productivity. The reality, however, is that cutting tools and parameters indicated for a certain workpiece material may not produce such desired results, and often the reason is variability in material composition.

To better understand how the five properties affect machinability, Seco partnered with steel suppliers and other metalworking-related companies to develop an analysis system that measures workpiece properties. The system charts data from quantitative measurements of the five material properties on a five-pointed grid or pentagram with low values appearing near the center and high values toward its borders. The area enclosed by the data points provides a graphic image of the particular material’s tendencies. Using the pentagram, machinists can better match tool features and cutting parameters to the actual properties of the workpiece.

Several common guidelines have resulted from Seco’s analysis system.

• Material adhesion tendencies create a need for tough tool substrates with tough coatings, sharp edge radii and high rake angles as well as cutting conditions aimed toward temperature control. This means speeds high enough to carry heat away in the ductile chip. Adhesion tool wear patterns include micro chipping, built-up edge, flaking and notch wear. 

• Tools aimed at handling material hardness should have strong substrates (depending on the feedrates employed) as well as cutting edges with small rake angles applied at low feedrates and shallower depths of cut. Typical tool wear includes plastic deformation, chipping and breakage.

• Machining materials that tend to strain harden require tools with toughness and small nose radii and cutting edge geometries for low cutting speeds, high feedrates and deeper depths of cut. Prominent tool failure modes include plastic deformation, chipping and notching.

• Materials such as superalloys that exhibit poor thermal conductivity mandate the use of tools with high compressive strength, high rake angles and strong cutting edges. Low cutting speeds and feeds are typical. Tools usually fail via plastic deformation or simply from a higher-than-normal wear rate. 

• Tools intended for abrasive workpiece materials should be engineered with abrasion-resistant substrates and strong cutting edges. Low feedrates and cutting speeds but high depths of cut are appropriate. Wear mechanisms include flank and crater wear and notching.

For more information on how workpiece material properties influence the machining process, please feel free to contact me.

About the Author

Tim manages Seco’s indexable milling product line for Seco NAFTA. In his spare time, he enjoys playing golf and working out.

No Magic Bullet for Global Success Exists

Guest Blogger: Lisa Seidl, Manager of Marketing Communications

Last month, the Society of Manufacturing Engineers (SME) invited me to attend the Detroit Economic Club’s monthly luncheon at the Detroit Marriott. The guest speaker was Mary Barra, CEO General Motors Company. Her topic was Driving Transformation and Economic Growth.

I was quite proud to be in the audience for a couple of reasons: 1) being a female in the manufacturing industry and; 2) working for a Michigan-based manufacturing company. I have not heard many speeches from Mary, other than 5-second snippets on television regarding GM’s recall issues. She is very impressive in the fact that she is so down-to-earth. I came away so energized by her talk, that I wanted to talk more about it!

She explained that her vision for General Motors is to become the global leader in the auto industry; not just ok or second best – The Best! She realizes this will take time, it will not happen overnight and there is still a fair amount of work to do to achieve this. There is no magic wand. It will take dedication and hard work to get through the current recall issues. 

Mary highlighted that to achieve these goals, GM’s culture must shift towards problem solving together, being candid with each other and having a tenacity to win. Global strategies must ensue and she has a true passion for the company. One of several current GM innovations is V to X technology – a system where vehicles talk to one another. This will appear in the next-gen Chevy Volt 2015. GM is striving to be the global leader through electrical vehicle technology. They plan to invest $1.8 billion in engineering and electric technology. A new manufacturing facility will be established in Warren, Michigan to house production of the complete electrical drive system.

Mary went on to give us a look into her personal life. After graduating from Kettering University in Michigan, she went on to Stanford in Silicon Valley for her secondary degree.  She is passionate for Science, Technology, Engineering, Math (STEM) programs. She described how the excitement and awareness for students to get involved with STEM begins with junior-middle school children.

When asked if she could give unconventional advice on what it takes to become a female CEO of a Fortune 100 Company, she responded “do what you love, work hard!” Her role models were her parents. Her Dad retired from GM as a diemaker and her mother was a bookkeeper. They both worked hard to give their children a better life. Mary’s favorite car of all the GM vehicles she has driven is the Cadillac CTS, because of its technology, design and performance.  She does, however, also love the Camaro.

In summary, I was most impressed with the fact that Mary did not have a magic bullet for success. She attributed hard work, collaboration, and passion for what you do every day to succeed. She truly is the epitome of a Woman in Manufacturing; and I could relate.

About the Author

Lisa is the manager of marketing communications for Seco Tools, LLC. She manages North American activities to encompass advertising, trade shows and machine tool builder events, communications and public relations. She and the MarComm team provide sales and distribution support with product launch introductions and promotional collateral. She also works globally with corporate brand identity to ensure the integrity of the Seco brand internally and externally. In her spare time, she likes to golf and cheer on the Detroit Red Wings hockey team. 

5 Steps to Improving Production Economics

By Todd Miller, Manager of Product Marketing

The goal of any machining operation is to produce accurate parts at the lowest cost, thereby maximizing profitability. The traditional way to lower machining costs is to accelerate production rates with more aggressive machining parameters, usually focusing on faster cutting speeds. That approach, however, does not recognize significant cost factors including the expense of scrapped parts and production downtime. Use the following 5-step strategy to balance productivity and manufacturing costs.

1.  Focus on the Costs You Can Control

Some elements of manufacturing costs are beyond your control. Workpiece material type is dictated by the end use of the machined component. Likewise, costs for machine tools, maintenance, and the power to run them are basically fixed, usually involving ongoing payments. Your strategy for increasing production economics, therefore, should focus on the variable costs such as machining process elements like which cutting tools you use and the parameters in which they are employed.

2.  Find Optimal Parameters

There is a common misconception that simply increasing cutting speeds will produce more parts per period of time and thereby reduce manufacturing costs. While using higher cutting speeds can increase production rates, it may also result in higher tooling and machine tool costs. Finding optimal parameters is essential and requires a balance between reduced cutting speeds and proportional increases in feed rate and depth of cut. The ideal is to use the largest depth of cut possible to reduce the number of cutting passes required and machining time. At the same time, maximize the feed rate, albeit carefully so as not to negatively affect workpiece quality and surface finish requirements. When a stable and reliable combination has been reached, cutting speeds can be used for final calibration of the operation.

3. Reduce Machine Tool Costs

Higher speeds initially drive down machine tool costs because the machine tool is producing more parts per period of time, therefore more revenue can be applied against its fixed cost. However, as speeds rise beyond a certain point, machine tool costs begin to increase. Tool life becomes so short that the decrease of the machine tool cost has a smaller effect than the fast increasing costs of tooling and downtime for tool changes. In addition, extremely high cutting speeds and very aggressive machining parameters in some cases can add to machine tool costs for maintenance and even result in downtime caused by unanticipated machine failures.

4. Follow A Model of Efficiency

American mechanical engineer F.W. Taylor once developed a model for determining tool life that shows that for a given combination of depth of cut and feed there is a certain window for cutting speeds where tool deterioration is safe, predictable and controllable. When working in that window, it is possible to quantify the relation between cutting speed, tool wear and tool life. Following this model brings together cost efficiency and productivity and provides a clear picture of what to aim for when defining the optimum cutting speed for an operation.

5. Establish a Stable Machining Process

The key to maintaining productivity and part quality and avoiding scrap is establishing a stable machining process. Create an optimum production environment by choosing the tool material, coating and geometry best suited to the workpiece and operations at hand, and optimize the machining CAM program, toolholding systems, and coolant application. Be sure to integrate workhandling automation such as pallet or robotic part load/unload systems into the process as well, because handling of raw and finished part stock can consume significant amounts of machine downtime.

Want to learn more? Please contact me, and I’ll help you create a balanced production strategy for your operations. 

About the Author

Todd is the manager of product marketing for Seco Tools, LLC. He oversees the product marketing team and works with the company’s sales department to further enhance the customer experience. He and his team also support product introductions while working globally on new product testing to ensure customers gain access to the industry’s most advanced tooling as quickly as possible. In his spare time, Todd likes to bowl and cheer on the University of Michigan football team. 

Simple Steps to Environmentally Aware Productive Machining

By Todd Miller, Manager of Product Marketing

In a world where energy is a rare, expensive commodity and pollution is a continually growing concern, there’s a growing need to machine components in a more efficient, environmentally responsible, “green” way. 

When machining complex components from high-performance workpiece materials such as nickel-base alloys, ultimate productivity in many cases is not of primary importance. The operations focus more on reliably producing dimensionally and qualitatively perfect parts. That is not to say economic and environmental considerations are irrelevant, but technological productivity and process security challenges are so prominent that efficient, green machining is not the top priority.

The story is somewhat different with simpler parts and more common workpiece materials such as steels and cast irons. Today, steels and cast irons make up the bulk of the materials machined worldwide, and all indicators show a stable situation in the tonnage that will be machined in coming decades. Employed across all industries, steel alloys offer a very good price-performance ratio in terms of cost, strength, and ease of machining.

Wide application and long familiarity have made the purely productivity-oriented aspects of steel machining less crucial. Manufacturers know how steel behaves and are rather sure they can create solutions that will guarantee good productivity.

As a result, our customers who machine steel are increasingly interested in the economical and environmental consequences of their machining operations beyond technological productivity issues.

Research institutes and universities around the world are examining ways to perform machining in a way that puts less load on the environment, namely using less energy and making less waste.

Part of the process involves gaining an overall perspective on the machining process. For example, we have found that workshops do not always realize that energy costs, specifically of electricity, are on the same or even somewhat higher level as cutting edge costs, expressed in cost per minute. Electricity costs include not only operation of a machine’s spindles and axes, but also CNC units and auxiliary equipment such as coolant and workhandling systems. 

There are many ways to reduce the energy consumed in the cutting process itself. Application of certain insert geometries, for example, can contribute to energy conservation. Where use of a sharper geometry is appropriate, 1-degree extra positive rake angle can reduce energy consumption by 1.5 to 2.5 percent.

Manipulating cutting speeds represents another opportunity to save energy. Productivity is the traditional goal in machining, and achieving it has almost always involved employing higher cutting speeds. However, one way to reduce energy consumption is to lower cutting speeds and proportionally increase feed rates and depths of cut.

If a machining application permits working with a combination of lower cutting speeds and higher feed rates and depth of cut, at least three benefits result. One advantage is that less energy is required to remove material from the workpiece. We have found that a one percent reduction of cutting speed reduces energy consumption by five percent; a one percent decrease of depth of cut combined with one percent increase of feed rate reduces energy consumption by two to three percent.  

Another benefit of lower cutting speeds can be longer tool life. Fewer cutting edges or inserts are consumed over a certain amount of time or over a certain number of workpieces. There’s a reason indexable tools have historically been called “throwaway” inserts; at the end of tool life, they end up as waste in the environment. At slower speeds in combination with other cutting parameter adjustments, however, fewer inserts are consumed to do the same amount of work.

A third advantage of the application of lower cutting speeds is a reduction in the heat generated in the metalcutting operation. In addition to contributing to longer tool life, reducing heat also lowers the cooling requirements of the cutting system and less coolant is needed. That is environmentally significant because used coolant is full of metals, lubricants and other contaminants and poses particularly troublesome and expensive disposal problems.

Of course, reducing the environmental impact of metalcutting operations goes far beyond tools and tooling systems. Complementary efforts to improve the environmental status of machining include recycling of chips and used carbide, moves to minimal-coolant or dry machining processes, and even research into use of workpiece materials that themselves require less energy to make. Productivity will always be the ultimate goal in metalcutting and manufacturing overall, but analytical thinking and simple actions can make productivity go hand-in-hand with resolution of environmental concerns.

About the Author

Todd is the manager of product marketing for Seco Tools, LLC. He oversees the product marketing team and works with the company’s sales department to further enhance the customer experience. He and his team also support product introductions while working globally on new product testing to ensure customers gain access to the industry’s most advanced tooling as quickly as possible. In his spare time, Todd likes to bowl and cheer on the University of Michigan football team.