PCD Vs Carbide who has better value?

PCD Vs Carbide who has better value?

PCD drills are considered high-end cutting tools, due to their rather complex manufacturing process and their higher market price compared to regular Tungsten Carbide drills.
In this ever-evolving composites materials market, the number of applications increase constantly, not only for the traditional aerospace segment, but also for Automotive, Wind turbines, Marine, Infrastructure and sports.
The use of PCD drills in composites is crucial for hole quality, process stability and cost effectiveness.
In this article we will explain why PCD drills are the best option an end user can choose for his composite application

You can divide the manufacturers of composite materials parts, which require hole making, into 3 types: End-users who use mainly PCD drills including regrinding services; End-users who use mainly CVD drills; End-users who use mainly carbide drills.

Tools price Vs. Process cost

While most buying decisions are price driven, there is no argument about end-users with low volume usage of drills and the best option for them probably is to search for the lower priced tool which complies to their requirements. In most of the times, it would be a Tungsten Carbide tool, which considered economical in price.
However, when large number of holes or large number of parts are about, the measurement of tool price only may be misleading. It is advisable in this case to look in a wider perspective.
The cost of cutting tools in an average manufacturing plant may vary between 5-10% of production cost, therefore saving the money on a chipper but less efficient tool is not worthwhile in most cases. The best measurement of tool effectiveness is by checking the entire machining process while measuring the cost of the tool divided by number of meters (in case of an endmill) or number of holes (in case of a drill).
When using CVD drills, the measurement is straight forward, by dividing the price of the tool to the average number of holes it is making. This would be the normal cost of the drill.
In case of using PCD drills, this measurement is not enough, since PCD drills can be resharpened few times and an overall life expectancy and overall number of usages must be measured.
But before we discuss this further, let’s try to remember the differences between Tungsten carbide, PCD tools and CVD diamond coated tools.

PCD Vs CVD Vs Tungsten Carbide

PCD (Poly Crystalline Diamond) is produced synthetically by sintering together many diamond particles, usually in the size of 2 to 30 microns of a meter, with a metal binder (usually Cobalt) at high temperature and high pressure. The hardness of the PCD is at the range of 6500-7000 Hv.

CVD Diamond (Chemical Vapor Deposition) – is a process of
coating Nano diamond particles on a Tungsten carbide substrate (tool) applying a typical layer thickness of 6 to 14 microns of a meter. The hardness of the CVD Diamond is at the range of 8500-9000 Hv.

Tungsten Carbide (TC) is a hard material compound with W and C double the density and stiffness of steel, used as sintered with cobalt as the binder, mostly to produce cutting tools. Typical hardness is 1500-1800 Hv.

Comparing these 3 tool materials, it is evident that PCD and CVD are much harder than Tungsten Carbide therefore much more wear resistant. There is an advantage to the CVD diamond coating in terms of hardness on the PCD, though much smaller.
When delamination is the failure criteria, CVD diamond drills are likely to perform better than the PCD wafer (segmental) drills due to the superior hardness of the cutting edge in minimizing delamination at the hole exit.
This is one of the major concerns in the drilling of composites in highly engineered parts in the Aerospace.
The TC drill is likely to wear very fast due to much lower hardness, so it creates more deflection and delamination than the PCD and CVD drills. It is known that tool life differences between TC tools and Diamond tools can be up to 25 times in favor of the diamond.

When hole diameter is the failure criteria, then the PCD drill is likely to hold longer than CVD drills. The reason for this is since CVD diamond is a coating implemented on top of TC substrate. When it eventually peels off, it would expose the tungsten carbide underneath and edge wear will accelerate rapidly.
The PCD, on the other hand, is a solid diamond. Wear development rate is rather fast at the very beginning when edge radius develops but then it stagnates for long period of time.
Another example where PCD have an advantage is when drilling a stack material like CFRP/Aluminum, where the exit hole is in the Aluminum. Delamination is a non-issue in this case, therefore PCD drill would be first choice since it will hold hole accuracy longer and can also be reconditioned few times (unlike CVD drills).
Another major advantage of the CVD diamond drill would be design flexibility. The CVD drill is manufactured in 5-6 axis grinding machine to a complete geometrical design and later is being diamond coated, whereas most of PCD drills in the market are based on straight segments which limit the design flexibility.
Design flexibility is critical when building a point geometry to tackle composites.

Wafer PCD vs. Full-nib PCD

Now we must explain the two different types of PCD drills: the Wafer drill and the Full-nib drill.
In the wafer (segmental) drill, PCD segment is in the drill center and drill geometry is built around it, while being limited to its shape and size.

On a Full-nib PCD drill, on the other hand, the PCD has a cylindrical solid shape on top of the carbide shank, therefore drill point design has no limitations.
Most of hole sizes in composites are in the range of 2.5mm to 8mm in diameter. This is the range of diameters where PCD Full-Nib drills can be most efficiently manufactured and utilized, since larger diamond nibs are quite expensive.

The new Helicon Full-nib PCD drill

Telcon has developed the New Helicon Drill for extended tool life, accuracy and repeatability while maintaining delamination-free results.

Unlike PCD wafer drill, The Full-nib PCD allows for flexible design. The new Helicon is designed with 2 point-angles with slower, more gradual penetration into the material.
The consequence of that is lower thrust force on the material and much lower delamination and deflection of the composite materials.

Case Study comparing PCD vs. CVD vs. Tungsten Carbide drills:
The application is drilling a CFRP unidirectional material, 5mm in thickness with diameter 4.87mm (.191″).
4 drills were tested:

1. A tungsten carbide uncoated dagger style drill 4.87mm.
2. A Helicon PCD Full-nib drill 4.87mm.
3. A PCD wafer drill 4.87mm.
4. A CVD diamond drill 4.87mm.

test setup

Drilling cutting conditions are based on common practice in drilling composites.

Test criteria is the size of generated Delamination. Failure occurs when delamination is more than 1mm further from hole circumference.

Drilling results were monitored every 200 holes for the diamond drills and every 100 holes for the TC drill. Then, holes were checked and marked for G/NG.
Final test results are gathered in the table and diagram below:

It is evident that the Tungsten carbide drill has much lower tool life as expected. The reduction in diameter from 1st to last hole is also the largest.
The Helicon drill has the best tool life while the CVD drill is second. The Wafer drill is approx. 50% in life compared to the Helicon drill. It is noticeable that the CVD drill has higher hole
diameter reduction than the PCD drills.
Cost comparison:
To better emphasize the significance of these results, let us make a cost comparison based on this test:

Summary and conclusion:

1. It is shown that PCD Full-nib drill, Helicon, is superior in tool life and normal cost (cost per hole).
2. It is shown that CVD drills are a very good solution when it comes to preventing delamination, although cost per hole is slightly in favor of the Helicon Full-nib drill. However, when hole accuracy is held within thin boundaries, the Full-nib drill outperforms the CVD drill.
3. It is also shown that the use of Tungsten carbide drills cost 3 times more than the use of PCD Full-nib drill, therefore advisable to be used only where there are fewer holes per part or lower number of parts to produce.
4. Setup time is excluded from this comparison, however if to be added, differences would be even higher, since tungsten carbide drills would need much more frequent replacements and will consume more machine idle time.
5. Feed rate comparison is excluded as well, and if considered, the Diamond  drills are 67% faster in table feed, so machine time can be saved.

PCD Countersink Vs. Carbide Countersink

Both PCD and carbide countersinks are commonly used in assembly and manufacturing processes, but what are the advantages of each type? what is the use case and when will we need to make the choice? in this article we will cover some of these questions in depth.

What is a Countersink tool?

A Countersink (in short, CSK) is a cutting tool with edges tilted to a certain angle to create a chamfer at a certain size. The chamfer is mostly at the end of a hole in a manufactured part. The chamfer holds the head of a connecting element such as a bolt, rivet, or a screw, to have the head of this element align with the part surface.

What are Countersink tool types?

There are multiple applications for Countersink tools, in almost every industry, however we would like to focus on the usage in the aerospace airframe industry.

Countersink is a very common tool in the assembly lines of airplanes, since all body parts are attached and connected with rivets. The head angle of the rivet is 100 or 130 deg mostly and the Countersink tool angle is built accordingly by the Countersink manufacturer. Countersinks can be either with an integral pilot which is a part of the Countersink body, or with an exchangeable pilot, where the pilot is a made separately and inserted to a central hole in the Countersink . The pilot stabilizes and centers the position of the chamfer relative to the existing hole centerline in the part. The Countersinks are being held inside a stop-cage device, which allows setting up the depth of the Countersink penetration, hence the size of the chamfer given in the spec.

What applications with Countersink are at the airframe assembly lines?

There are two main applications for Countersinks, one which involves connecting parts made from Aluminum and second, parts made from FRP (Fiber reinforced plastic). There can be also a combination of both. There is not much difference in the way the Countersink tools are used in these two applications, there is, though, a major difference in the Countersink type. While in Aluminum parts, recommended Countersinks are with tipped carbide segments, on the Composites parts, recommended Countersinks are with PCD tipped segments.

PCD Countersink VS. Carbide Countersink

Understanding the difference between PCD and carbide, can explain some common mistakes end users are making while using the wrong countersink type for their application.

Composite materials are extremely abrasive due to the hard fibers inside their matrix especially in carbon fibers (CFRP). Choosing a carbide tipped CSK for this application is mistake no. 1.

PCD is 3-4 times harder than carbide. This explains the wear resistance advantage of PCD vs. Carbide in cutting composites. PCD tools can outperform a carbide tool by at least 20 times and show consistent quality results over much longer time compared to carbide.

People often compare only tool price and while PCD CSK may cost 2-3 times the price of Carbide CSK, that is mistake no. 2.

When using PCD Countersink vs. Carbide Countersink you would benefit from:

1. Longer tool life by a factor of 20 at least.
2. Consistent part quality over much prolonged time.
3. Fewer setups.
4. PCD CSK can have the option of resharpening and re-use at least twice.

Let’s compare “apples to apples”:

One PCD Countersink would in average make 1500 holes in CFRP, while carbide will make around 60 holes.

If we consider 2 re-condition cycles for PCD Countersink , that is a total of 4500 holes in one life span of a PCD Countersink.

There should be no doubt now, that PCD Countersinks are much better for using on composites.

Telcon Diamond Ltd. manufactures both types of Countersink tools made from the best PCD and carbide grades.

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