Fully automated systems are a true advantage for today’s large manufacturers but with the increased productivity output and reliability comes big challenges from small chips which create stress for machinists, the workpiece, tools and machines.

When auto parts producer Masung in Mungyeong, South Korea went the next level up and updated their factory, they found that chips were becoming the bane of their existence and hampered the parts they were producing for the big Korean car makers.

What they found was a constant stream of alarms followed by machines automatically shutting off because of those nagging metal chips that would either wrap around the tool or become so long that other problems would stem from their rise out of the workpiece.

In order to remedy this constant stoppage to their production line, Masung placed a challenge to their cutting tool suppliers from Japan, Sweden and South Korea.

Up for the challenge and equipped with the right tools for the job, TaeguTec sat down with the production manager of this technologically advanced company that is responsible for important innovations in the automotive manufacturing sector to examine their machining process and figure out a way where they can increase productivity, cut cost and make sure that every step of the manufacturing line flows smoothly without interruptions.

While the rest of the companies could not deliver results, TaeguTec offered simple advice: simply change the inserts, do a few improvements in the work process and upgrade their tools.

Out of the plethora of parts Masung creates for Korean automakers, two were of extreme importance: the input shaft and the seven-speed double clutch transmission.

The input shaft delivers power from the clutch into the transmission. To properly produce this quality part that can safely handle the stress of everyday driving, Masung setup 13 lines producing 100,000 input shafts per month.

Because of the complex machining process that entails setting the right cutting parameters mixed with choosing the proper cutting tool that would effectively break or control the size of chips, TaeguTec started Masung’s manufacturing improvements on one line. Since then, TaeguTec has improved four lines (at the time of this story) with the remainder slated for the near future.

To effectively machine the input shafts at a fraction of the cost while also increase productivity and eliminate slowdowns on the line, TaeguTec engineers applied their highly successful game-changer, the RhinoRush line, to machine input shafts made from SCR420HB and SCM920HVSI materials.

While other cutting tool companies were having problems recommending a small selection of tools to do the job, TaeguTec simplified the insert selection process by using four different kinds of chip formers; a feat that was not duplicated by other companies.

By doing so, TaeguTec’s RhinoRush eliminated those nasty long chips from forming and creating havoc on the assembly line. The results where exactly what Masung was hoping – TaeguTec increased the tool life and substantially reduced the size of metal chips like no other company could.

Out of the three lines TaeguTec had to improve, each line saved on average anywhere from 10 to 27 percent machining cost over the Japanese competition.

The RhinoRush line is a series of mini tuning inserts that meet the manufacturing industry’s needs of reduced machining cost. The 9 and 13 millimeter line of inserts are just as strong as the 12, 15 and 16 mm inserts but at a fraction of the cost and size.

What makes this tool stand out from the rest is not only the series’ small and durable size, but also its unique two directional clamping force that outperforms conventional ISO directional clamping force tools on the market.

Another tool the Asian metalworking giant applied to the process of creating better, safer and more reliable input shafts for Masung and Korean automakers is the T-Burst QuadRush Line.

With its four corners compared to the existing three corners Masung was using from another cutting tool provider, TaeguTec was able to improve tool life by 50 percent per corner. Moreover, the question of out of control chips during the grooving process was rectified.

TaeguTec’s T-Burst high-pressure coolant tool was designed to meet the groove-turning and parting machining needs of difficult-to-cut materials such as titanium, Inconel and other heat resistant alloys.

With the coolant outlet located on the upper jaw, directly over the insert, TaeguTec’s T-Burst high-pressure coolant, which is supplied through the tool holder’s internal coolant channel, shoots out enough force and speed to the insert’s cutting edge thus allowing for lubrication of the material and cutting tool, as well as effective cooling, excellent chip breaking and increased tool life while preventing built-up-edges.

The other process in need of improvement was the seven-speed double clutch used in more and more models which makes sporty driving performance possible due to its direct drive and lightning-fast gear changes.

The materials employed to produce these innovative transmission parts are SCR420HB and are used in many popular Korean passenger vehicles and SUVs.

Masung produces over 4 million DCT parts for Korean automakers so any slowdown in the manufacturing process will have detrimental affects to their bottom line.

Again, in order to remedy the creation of elongated chips, TaeguTec simplified the chip former selection and replaced the CNMG 12 and DNMG 15 inserts used with RhinoRush TNMG 13 six-corner inserts, a process that improved the line and reduced the cost by 30 percent.

Masung has been so pleased with the overall performance by TaeguTec’s tools and service that the Asian metalworking giant has increased its presence from 10 percent to 40 percent at the time of the visit with more being phased-in every month.

In machining, a problem like poor chip manageability can cause massive challenges no matter the size of the manufacturing company. For TaeguTec, reading chip formation is like reading tea leaves – this is where answers are found in order to control turning cost, tool life and surface finish, all factors that increase the overall manufacturing process and heighten process security.

In automotive suspension, a steering knuckle (or spindle knuckle or axle arm or stub axle) is that part which contains the wheel hub or spindle, and attaches to the suspension components. Materials used for knuckle parts are basically Cast & SG Iron and Alloy Steels. Depending upon the type of vehicle, the material is chosen. We can widely see Forged Steel as a material in Heavy vehicle (Trucks & Buses) and SG iron in passenger cars.

The major amount of material removal in knuckle is done by face milling, drilling & gap milling.
Face milling and drilling can be addressed with standard products. Application like gap milling really calls for an engineered solution according to the knuckle design.

GAP MILLING – ROUGHING
Material: Forged Steel (Common in Heavy vehicles – Trucks & Buses)

Approach 1 : Special purpose machines (SPMs) with good power availability ( i.e : 11 kW and above ).
SPM approach is more suitable for transfer lines where only one particular operation is performed. This can be used for rough machining of Gap where the stock levels will vary from 2 – 8 mm. This option is capable of running at low to moderate cutting conditions.

Example 1: The cutting speed can be from 80 ~ 120 m/min and table feeds can be from 60 ~ 100 mm/min. Here we can use the options of inserts with cutting edges on both sides.

Example 2: Square insert with 8 cutting edges with specific corner radius requirement. In this combination we can look at using corner radii up to 3.2 mm. When the corner radii requirement is more than 3.2 mm, having more number of cutting edges becomes a limitation due to increase in the insert size which will result in less number of teeth and higher cutting resistance. Here we go for single sided inserts which can be triangular shape or square shape with 3 and 4 cutting edges respectively.

Case Study
Application: Rough machining of Knuckle Gap:
Knuckle gap : 112 + /-0.25 mm
Cutter used: Dia 250 mm Right Hand & Left Hand for the front and rear sides. And D 250- 14 mm thick + Dia 250; 59.5 mm thick cutters for inside milling.

In the above combination, we used double sided square inserts in all the cutters. The outer cutters have inserts with chamfer and inside, GAP machining cutters have R3 corner radius. This combination can give a tool life of 200 ~ 250 components per edge set at a cutting condition of 80 ~ 100 m/min and a feed of 60 – 120 mm/min.

We should keep in mind that the work piece clamping rigidity plays a vital role in this set up. The clamping of the work piece must be good along with machine capability because we are not only machining the GAPS, also the front & rear sides.

Approach 2: Machining Center route
This approach is more suitable for controlled depth of cuts. The depth cuts cannot cross 3~4 mm. When the DOC is higher we go for more number of passes. This particular approach is good for the recent market trend where there is high demand for model change. The machine can accommodate the model change by changing the fixture locating plates and clamps.

There will be the limitation of cutter diameters and tool holding capacity of the machine. The radius formation inside the gap will be by interpolation of the cutter. Here we are forming the radius of R158 by using a Dia. 240 cutter. This kind of solution can be used at cutting speeds between 100 ~ 180 m/min and feed rate of 200 – 400 mm/min with controlled depth of cuts.

We have to be very cautious on the tool length in this case. If the tool length is longer due to the knuckle design or the clamping mechanism, we need to optimize the cutting condition.

Approach 3 (In case of clamping rigidity and machine power being a limitation)

Case Study:
Rough gap Milling: Knuckle
Material: Forged Steel
Machine: SPM – Special adaptation/ Flange Type Mounting.

Cutters used: Dia 350 mm Right hand & Left Hand with corner radius 5 mm.

Here we can clearly see that we have used triangular inserts with 3 cutting edges where the cutting forces will comparatively lower than the double sided inserts. The corner radius requirement on the component is R5 and the cutter diameters are also bigger.

Here we use similar cutting condition and achieve good tool life!

GAP MILLING – FINISHING
When it comes to finishing of the knuckle GAP, irrespective of SPM approach or Machining Center approach, there is a wide range of insert choices.

a) Tangential mounting of inserts on the cutter (refer the below picture). You can see the cutter is chopped from both sides in order to accommodate on the machine ATC.

This kind of tangential mounting gives good surface finish values between Ra 1.6 ~ 2.3 and the flatness on the walls lesser than 0.05 mm . We can use cutting condition Vc 150-200 m/min and feed 0.07~0.15.

It is always better to keep stock levels for finish as 0.7~1.2 mm considering the corner radii of the inserts.

b) Radial mounting type with triangular inserts:
The below design is for SPM machine where 2 different cutters are mounted on the arbor with a spacer and used for finishing of the GAP. For machining center, there can be a single cutter with inserts on both sides.
We can machine the component by Z axis movement or by B–axis rotation.

Lug Machining in SG Iron (usually smaller knuckles common in passenger cars and light vehicles.)

Machining of Grey-Nodular iron knuckle are simpler compared to the steel ones because :

1. Machinability is easy. Machining areas are smaller comparatively
2. Chip evacuation is not at all a concern
3. Size of the knuckles are also smaller – Clamping of the part is simpler
4. Dry cutting can be performed in order to achieve higher life and avoid coolant usage.
5. Moderate machine rigidity is good enough. BT40 / ISO40 machine also can be used.

Cutter designs that can be looked at:

Case Study:
Limitation: BT40 machine with 7 kw / Stock removal:2~3 mm .
Customer demand: Low cost / piece

Especially these kind of smaller knuckles are machined in MCT only. The cutting speeds can be from Vc 200 ~300 m/min, and feed can be 0.1 ~ 0.2 mm/ z.