PCD and PCBN ISO Tipped Inserts

Introduction

Many modern materials such as high silicon aluminiums, glass filled epoxy resins and even some hardened steels may now be machined utilising the enormous benefits of polycrystalline diamond and cubic boron nitride superabrasives. In order to make these superabrasive cutting materials more 'user friendly', Hamilton Lichfield manufacture tipped inserts which are interchangeable with the conventional ISO range of tungsten carbide and ceramic cutting inserts now found in most machining environments. Therefore, whenever a change of workpiece may dictate the use of superabrasives, the appropriately tipped PCD/PCBN insert may now simply be fitted to the current toolholders, with minimum machine downtime.

In practice the vast majority of carbide inserts for turning, boring, milling etc. may be tipped with PCD/PCBN, to provide the desired cutting edges. However, very small tips which are impractical to braze may be produced 'full form', i.e.: the correct shape of the insert is cut from a solid disc of the superabrasive material.

The following notes are intended as a guide to selection, price coding and ordering of Hamilton Lichfield's tipped inserts.

1. Superabrasive Materials

There are many different types of tip available in the market designed to cope with an array of workpiece materials but for simplicity these may be grouped as follows:-

• Polycrystalline Diamond (PCD).
• Polycrystalline Cubic Boron Nitride (PCBN) for rough machining.
• Polycrystalline Cubic Boron Nitride (PCBN) for finish machining.

PCD

PCD may be cost effectively employed to machine the following broad range of materials:

• Non-ferrous metals and alloys including, aluminium, copper, bronze, brass, green tungsten carbide, precious metals and MMC's.
• Non-metallic materials including, ceramics, reinforced plastics, hard rubber, chipboard, MDF's and other fibreboards, etc.

PCD may be used for both roughing and finishing work, although it is usually most beneficial when tight tolerances or high surface finishes are required combined with the need for exceptionally long tool life. It is available in three grades of increasing crystal size and toughness but with an attendant decrease of edge quality.

The finest grade is, therefore, only employed where superior surface finish is the main objective, the middle grade is the general purpose material giving long life with good component finishes; the coarse grade is used where maximum abrasive resistance is required and where finish is not critical, for example the machining of metal matrix composites.

Hamilton Lichfield will be pleased to offer advice on the selection of the best grade of PCD and cutting geometry for your particular application.

PCBN

If polycrystalline diamond has a major disadvantage, it is that being carbon based, it has an affinity to the free carbon found in most ferrous materials and is therefore generally unsuitable for machining steels and iron based materials. For this reason a range of products has been developed based on polycrystalline cubic boron nitride which have been demonstrated to be extremely cost effective especially with the harder ferrous materials (45-65 HR). Examples of materials that may be considered for machining with these inserts are listed below:

• Hardened Steels
• Martensitic and Chill Cast Iron
• Hardened Bearing and Cold Work Tool Steels
• Martensitic Stainless Steels
• Hard Facing Alloys which are Cobalt, Nickel and Iron based
• Pearlitic Grey Cast Iron

PCBN For Rough Machining

Different types of PCBN exist for the rough machining of the materials listed above which are usually selected on the basis of the required amount of stock removal.

For roughing cuts in excess of 1mm depth the PCBN is usually supplied in the form of solid ISO tips for use in a clamp type tool holder, designed for use with negative top rake geometry. It is also usual to provide a strengthened cutting edge by means of a lapped or honed 'T' land.

Where roughing cuts up to 1mm only are to be taken or when the applications require positive tool geometry, a brazable type of PCBN may be employed. In these cases the inserts are fabricated in a similar manner to diamond tips but usually with a polished 'T' land.

PCBN for Finishing

A specific form of PCBN with reduced CBN content is supplied for use on fine finishing of hard ferrous materials. This material is capable, given the correct machining parameters, of producing turned finishes equal to those of ground components. The attendant cost savings found from switching from grinding to turning are often very dramatic. Again, the inserts are fabricated in a similar manner to those in PCD.

2. Insert Shape

Hamilton Lichfield follow the normal ISO convention for describing insert shape and geometry, for example an 11mm triangle may be designated as follows:-

T C N T 11 02 04

T = Shape (triangular)

C = Insert clearance angle (7°)

N = Tolerance class (N)

T = Type of insert, i.e., Hole and Chipbreakers

11 = Edge length (11mm)

02 = Insert thickness (2.38mm)

04 = Radius (0.4mm)

A full breakdown of insert nomenclature can be found in any insert manufacturers catalogue.

In addition to the insert description we need to know the size and position of the PCD/PBCN tip. The following illustrations detail some of the more common inserts and show the normal position of the abrasive layer. Where the abrasive length is not confined by the size of the insert, the edge length may be supplied to customers needs. Table 1 shows our standard range of products.

3. Pricing

The price of the tipped inserts depends upon both the insert cost and the amount of PCD/PCBN supplied, Table 1 below lists the common inserts supplied, with their price codes, based on 'M' and 'U' class inserts. An additional charge of up to 10% may be made if the close tolerance 'G' class is required.

TABLE 1

PCD
STYLE	SHAPE	ABRASIVE	CODE PREFIX	MINIMUM CUTTING EDGE LENGTH 'L'
				3mm	4mm	6mm	10mm
T	Triangular	Diamond	TMD-	TMD-3	TMD-4	TMD-6
S	Square	Diamond	SMD-	SMD-3	SMD-4	SMD-6	SMD-10
C	Rhomboid	Diamond	CMD-	CMD-3	CMD-4	CMD-6
D	Rhomboid	Diamond	DMD-	DMD-3	DMD-4	DMD-6
V	Rhomboid	Diamond	VMD-	VMD-3	VMD-4	VMD-6
				CUTTING DIAMETER
				8mm	9mm	12mm	13mm
R	Round	Diamond	RMD-	RMD-8	RMD-9	RMD-12	RMD-13
PCBN				FOR >1mm STOCK REMOVAL
				MINIMUM CUTTING EDGE LENGTH 'L'
				3mm	4mm	6mm	10mm
T	Triangular	CBN	TMC-	TMC-3	TMC-4	TMC-6
S	Square	CBN	SMC-	SMC-3	SMC-4	SMC-6	SMC-10
C	Rhomboid	CBN	CMC-	CMC-3	CMC-4	CMC-6
D	Rhomboid	CBN	DMC-	DMC-3	DMC-4	DMC-6
V	Rhomboid	CBN	VMC-	VMC-3	VMC-4	VMC-6
				CUTTING DIAMETER
				8mm	9mm	12mm	13mm

NOTES:

1. 'G' Glass inserts are 10% above standard product prices
2. Prices for full form PCBN roughing inserts on application

4. How to Order Tipped Inserts

In order to specify the product you require we would need to have the following information:

1. The insert designation - ISO code (usually on the makers packaging).
2. The type of abrasive (Diamond or CBN).
3. Length of required PCD/PCBN cutting edge.
4. Any special features eg: Top rake or radius different to the code etc.

In the event of all of the factors not being known, Hamilton Lichfield are equally happy to work from first principals and then we would need you to specify details such as:

1. The material to be machined.
2. A used sample of the insert currently being employed.
3. In the case of a milling cutter the number of tips required.
4. Component drawings if available or details of stock to be removed, smallest radii to be machined, etc
5. Details of the machine to be employed with speed and feed range available.

Should it be more convenient, we are always happy for our technical staff to visit and assist in assessing the application and where necessary arranging for suitable trial tooling.