In the past couple of decades, automotive manufacturing has evolved significantly. Consumer appetite for greater performance, fuel-efficient and environmentally-friendly vehicles has become larger than ever before.
The trend in today’s automotive manufacturing requires short production time yet a high degree of flexibility. To accommodate more complex machining, custom tooling can offer an additional solution to manufacturers seeking maximum results.
Productivity Improvement in Drilling
To accelerate productivity, an increase in cutting speed and feed rate is often required. However, by simply increasing the speeds and feeds, greater cutting force is generated, which in turn creates more vibrations that puts higher stress on the tool cutting edge.
With excessive vibrations and stress, poor hole quality and short tool life become the common unfavourable end results. Machines are also trending to become more compact along with a more simplified jig setup. With a less powerful machine and a less rigid setup, speeds and feeds cannot be easily raised.
There is a clear correlation between the cutting velocity and feed rate with thrust force and drilling torque. When the drilling thrust exceeds the material bond strength, damages can be caused around the hole.
To increase productivity in drilling by cutting speed and feed rate acceleration, low thrust is an absolute prerequisite.
As shown in Figure 1, thrust force is the highest point in the center of the drill. To suppress thrust force, drills are designed with wider chip pocket to improve chip evacuation as shown in Figure 2.In this case study we will examine two applications where the wider chip pocket geometry was able to facilitate greater performance in terms of efficiency and quality.
Application 1: Crankshaft
The challenge that the manufacturer faced was to further improve cycle time in S40C.This was done by adopting a custom 10 mm diameter TRS 3-flute carbide step drill with low thrust geometry. The results saw cutting speed and feed improved by 2.5 times. The cutting speed was increased from V = 80 m/min to V = 100/min, while feed rate improved from 509mm/min (f = 0.2 mm/rev) to 1,273 mm/min (f = 0.4[h1] mm/rev).
Cutting speed and feed rate are the main parameters that influence thrust force and hole quality. An increase in cutting speed led to the increase of drill wear and thrust force. With the adoption of a custom step drill, the manufacturer was able to control thrust force for higher productivity.
Application 2: Connecting Rod
The manufacturer’s aim was to minimise tool exchange frequency and to eliminate reamer processing time. The solution was to adopt a custom drill with low thrust geometry to reduce stress on workpiece, maintain high hole precision and eliminate the need of a reaming tool.
Reamers are generally used for finishing. With the adoption of a combo tool, a single tool was able to complete two different processes yet maintain the required hole accuracy. The result was a greatly simplified tool management and reduced cycle time.
Application 3. Ring Gear
Although the processing only required a short tapping length, the work material was difficult to machine, causing unstable chip evacuation. The tendency to generate inconsistent cutting chips resulted in tool damage and breakage.
The conventional spiral cut tap had a tool life of 300 holes. With the adoption of OSG’s XPF form tap, tool life was increased to 2,000 holes. As the forming tap forms screw threads through plastic deformation of work material, no cutting chips were created. With no cutting chips, chip evacuation troubles were completely avoided.
When the manufacturer shifted focus on creating better chip separation by reducing the speed rate, gouging of the threads occurred. The slowing of tapping speed generated less heat. However, it would also cause greater cutting resistance and tool wear.
By adopting a special threading design and surface treatment, the XPF significantly reduced friction, making it feasible for longer life at faster speeds in materials up to 35 HRC. This resulted in a reduction in torque and a considerable suppression of heat generation.
Because plasticity varies depending on work materials, do note that proper adjustment may be needed based on the hardness and required accuracy of thread.
Standard & Custom Tooling Solutions
The automotive industry has been evolving rapidly in recent years through the new discovery of materials and technologies, prompting the need of sophisticated cutting tools capable of accommodating these new requirements.
Not only are powerful standard cutting tools needed for the automotive industry; tailored application solutions can also help give manufacturers an extra boost to their production floor.
APMEN Cutting Tools, Mar 2017