We’re all the beneficiaries of the end result of manufacturing processes in our everyday life. It is the lifeblood of technological advance and, simple, everyday items that make life what it is. One piece of the manufacturing equation that we’re all subject to – we’re talking 100%* of us (*this is not a formal result of any sort of poll/report), is the thread. If you’ve got something – anything with some sort of screw in it, you’re experiencing the product of manufactured threadwork.
That said, let’s put the spotlight on thread creation – one of the most tried and true technologies in global manufacturing.
Threads are accomplished by two general modes of action – cutting or rolling. One, as the name implies, removes material to accomplish the desired geometrical thread through a literal cutting/grinding process (thread cutting), the other applies pressure to a material to generate the desired geometrical thread (thread rolling).
Generally speaking, materials that are best rolled are difficult to cut and materials that are best cut are difficult to roll. That might be the best answer, honestly (a material fueled approach).
The Ins and Outs of Material Selection
We’ll state the obvious for the sake of transparency… Working with the correct material will ensure the overall success of the thread creation process. The softer the material, the easier it is to utilized the process of thread rolling. The harder the material, the more you ought to lean towards thread cutting/grinding as the best application in order to optimize the life of your die/tool.
The other variable here (and believe us, we’re not doing a super deep dive here, we’re just putting the general operative processes on the table…) is machine speed and how that factors in to your rolling and/or cutting process. As an example, sulfur and lead will allow for high speeds but can compromise the quality of the finish of your rolled thread operation. Other materials such as stainless steel, allow for an excellent thread finish but are harder to roll and may lend itself to a compromised tool life. Working with steel, bismuth, aluminum, or sulfur will produce flakes and slivers which needs to be considered and offset to minimize poor tool/thread finishes.
Hardness and plasticity are two key traits when deciding whether or not the best operative approach will be thread rolling vs. cutting. By-and-large, the idea behind thread rolling is that it relies on the plasticity of the base material which lends to the ability to deform, or, rather, permanently imprint the desired shape into the workpiece through an imprinting die/head.
Benefits of Thread Rolling vs. Cutting
We’re not here to choose favorites. The matter in which you get from point A to point B is entirely up to the operator/engineer, but, we’d be remiss to not mention the inherent benefits of applying pressure to achieve a result vs. cutting into the physical material.
Not to dumb it down too much, but cutting can occur on just about anything. That said, a material that has a higher degree of plasticity is probably best served with the rolling process because cutting it might lead to gummed up edges on the threads (which is obviously an undesirable trait as far as threads go…)
Assuming the workpiece material meets the yield and flow requirements for rolling, the process offers several advantages over cutting threads. Compared to other production methods, rolled threads have improved physical properties. The cold working that takes place in the thread rolling process produces an increase in tensile strength and a better surface finish than is achieved with cutting operations.
Studies of shown that thread rolling improves the tensile strength of the material (metal) by 30% or more compared to that of traditional thread cutting/grinding methods. Improved fatigue strength of the finished product also increases by 50-75% via the rolling process which is obviously better for the application/longevity of the finished product.
Three basic thread rolling practices* are:
Axial Thread Rolling – Axial thread rolling accomplishes its work by moving from the front (tailstock) of the part along the spindle centerline. In a single pass, three (up to six) rollers, synchronized by a planetary gear system, impart the desired OD thread shape, depth and pitch onto a workpiece.
Tangential Thread Rolling – The tangential roller head makes its threads by approaching the workpiece blank from the side. Sometimes called side rolling or cross slide heads, tangential thread roller are designed to roll threads by pushing, at a controlled feed rate, two fixed parallel rolls onto the rotating component.
Radial Thread Rolling – The radial thread rolling process utilizes two or three rolls to form a thread in a single rotation of the workpiece blank. The rolls on this type of thread roller are ground eccentrically. Starting with a flat on each roll, the thread form is progressive. A shallow thread form starts at one side of the flat and full form at the other side.
*Information sourced from Modern Machine Shop Magazine.
In a Nutshell
If you’ve got a project that requires some degree of thread production, utilize your trusted partners/sources to understand the pros and cons of both sides of the proverbial coin. As with many parts of the manufacturing process, the path you ultimately choose is decided by the unique variables the task at hand is faced with. From the perspective of thread production, the most efficient and economical method is thread rolling.
The process of thread rolling – depending on your needs – enables:
- Higher repeatability
- Stronger threads
- Better finish quality
- Quicker production times
- Increased mechanical properties
- Decreased waste
- Improved lead-times
- Bolstered bottom lines
We’re not saying that thread grinding, cutting, or chasing is inadequate and can’t provide a good ROI. We’re simply suggesting to consider what you’ve been up to and if that due process can be improved upon.
Afterall, one small change can lead to increased gain. At the end of the day, you won’t know until you take a closer look…
Thanks to all of you for lending us your time and filling us in on a little bit of what makes your unique operation tick. To read the full features on these fine companies, visit our online back issue archive. It’s all there on-demand.
Interested in having your company featured in a future issue of The Gateway Magazine? Give a shout! We love hearing all your stories and putting them to print. Here’s to 2020!