Part 1: Cutting and Forming

The way a material plate is cut at the beginning can directly affect the operations that follow.

Thermal cutting creates a heat-affected zone at the edge. Mechanical cutting leaves cold deformation, while waterjet cutting does not affect the material structure through the same mechanism as thermal cutting.

For this reason, the cutting method should be selected as part of the entire fabrication sequence, especially when the component will later be bent, drilled or further formed.

With high-hardness steel, an unacceptable cut edge, untreated burrs or an unsuitable bending radius may not cause immediate failure in the workshop. These areas can later become initiation points for microcracks or cracking during forming or after a period of operation.

1. Explanation of key technical terms used in this article

Before examining individual cutting and forming methods, several terms should be clearly understood because they appear throughout fabrication drawings, technical guidelines and workshop inspection activities.

Five terms related to cutting and bending

Technical term	Meaning
Burr	A sharp metal projection remaining on the edge after cutting
Microcrack	A very small crack at the edge root that requires close inspection to detect
Rolling direction	Direction of the steel grain, which affects the bending radius
Cold deformation	Change in steel caused by deformation at room temperature
Preheating for thermal cutting	Heating the steel before thermal cutting to control the cooling rate

Two additional concepts also need to be noted:

Technical term	Meaning
Heat-affected zone (HAZ)	The band of material adjacent to the cut that is affected by the thermal cycle
Minimum bending radius	The smallest permissible radius for the specific grade, thickness and rolling direction

In this article, preheating for thermal cutting refers to heating performed before thermal cutting. Preheating for welding is part of the welding process and is discussed in Part 2: Welding high-hardness steel.

2. The cutting method determines the edge condition and affects subsequent operations

Different cutting methods leave different edge conditions. These conditions directly affect bending and forming in the next stage.

Cutting method	Resulting edge condition	Effect on subsequent operations
Thermal cutting	A heat-affected zone is created, and the edge structure has been thermally affected	Greater attention is required if the edge will later be bent
Waterjet cutting	Does not create a heat-affected zone through the same mechanism as thermal cutting	More favorable when the component needs to be formed close to the edge
Mechanical cutting: shearing, punching	The edge is subjected to cold deformation	The edge may be more prone to cracking during subsequent bending

The cutting method should therefore not be selected independently of the work that follows.

If the component still needs to be bent, drilled or further formed, the material grade, thickness, cutting method and requirements of the next operation should be considered together.

The same material can have different edge conditions depending on how it is cut. A method that is convenient for cutting is not necessarily the most suitable for the next forming operation.

3. Thermal cutting: controlling temperature and cut-edge quality

Thermal cutting heats a narrow zone of the material to a high temperature while the surrounding steel remains at a lower temperature.

After cutting, the surrounding material draws heat away from the heated zone, causing it to cool rapidly. Where the technical documentation requires preheating, heating helps control the temperature difference and cooling rate.

Cracks may not appear immediately after cutting. Therefore, a freshly cut edge that looks intact is not sufficient to confirm that all fabrication conditions were appropriate.

3.1. Preheating according to the correct grade and thickness

Where the applicable documentation requires preheating, the temperature needs to be controlled before ignition and during the cutting process.

Control item	Requirement
Equipment	Heating equipment and a contact thermometer, not only temperature crayons
Method	Heat both sides evenly around the cutting line
Temperature threshold	Refer to the correct material grade and thickness range
Before cutting	Measured temperature on both sides meets the requirement
After an interruption	If the temperature falls below the required level, reheat before continuing

There is no single preheating temperature that applies to all high-hardness steels.

Before starting a fabrication batch, the correct material grade, thickness and applicable technical documentation need to be identified. A parameter used for a previous batch remains valid only if the current batch still falls within the same scope of application.

3.2. Preheating must remain within the permitted temperature range

Preheating is not simply about reaching a minimum temperature.

The temperature must remain within the range appropriate for the specific grade, thickness and fabrication method. A temperature below the requirement will not provide the intended cooling-rate control, while a temperature above the permitted range may affect the material condition.

Therefore, the required value should be taken from the current technical documentation rather than from a single memorized value applied to several steel grades.

3.3. Preheating requirements vary by cutting technology

Thermal-control requirements do not apply in the same way to every cutting method.

For laser cutting and nitrogen plasma cutting, preheating may reduce cut quality. These methods do not use preheating in the same manner as conventional thermal cutting.

Before applying any temperature requirement, the cutting technology and its corresponding technical guidance need to be clearly identified.

3.4. Inspecting the edge after cutting

The surface and edge quality of the steel should be inspected before the component moves to the next operation.

Item	Method
Inspection method	Visual inspection, hand inspection and appropriate measuring tools
Acceptable condition	Clean edge, no scale or deep burn marks, no detectable sharp projection by touch
Condition requiring correction	Rough edge, grooves or microcracks at the edge root
Action when unacceptable	Rework the edge; if cracking remains, remove the cracked area

An unacceptable cut edge may not cause an immediate problem at the cutting stage.

Damage may only appear when the component is bent or after a period of operation. At that point, the original cause may be difficult to trace if the edge condition was not inspected and recorded earlier.

4. Mechanical cutting and punching must remain within the permitted range

Shearing and punching can only be used within certain hardness and thickness ranges. Outside the permitted range, cracking may occur at the edge.

The applicable range must be checked against the exact material grade. Where mechanical cutting is unsuitable, other methods such as thermal cutting or waterjet cutting should be considered according to the applicable technical documentation.

Before selecting a method, determine:

material grade
thickness
cutting method
forming requirements in the next operation

This information helps avoid a situation where a component has already been cut but the resulting edge condition is no longer suitable for subsequent bending or forming.

5. Ceramics, fused cast basalt, two-component plates and hard compounds require dedicated fabrication methods

Processes used for steel plate cannot be applied directly to every wear-resistant material.

A single piece of equipment may use steel, ceramics, fused cast basalt, hard compounds or two-component plates at the same time. Each material group has different characteristics and requires an appropriate fabrication method.

Material group	Methods used	Methods to avoid
Ceramics, fused cast basalt	Diamond cutting discs or diamond-grit tools	Thermal cutting and steel tools
Two-component plates: steel backing with hard facing	Plasma cutting, air carbon arc gouging, silicon-carbide abrasive saw, abrasive waterjet cutting	Shearing, punching or drilling directly from the hard-facing side
Cured hard compounds	Diamond cutting discs	Methods similar to those used for ceramics

5.1. Plasma cutting two-component plates from the hard-facing side

For plasma cutting, the cut proceeds from the hard-facing side toward the steel backing.

The plasma jet naturally creates a bevel. Cutting in this direction places the bevel on the steel-backing side rather than on the working layer.

5.2. Air carbon arc gouging requires a suitable power source

Air carbon arc gouging uses direct current reverse polarity and requires a minimum open-circuit voltage of 60 V, with 80 V indicated as more suitable.

If the power source does not meet the requirement, the arc may extinguish during operation and leave pits on the surface.

5.3. Do not drill directly from the hard-facing side

The hard-facing layer referred to here has a hardness range of 700 to 820 HV. Conventional drill bits and milling cutters are not suitable for drilling directly through the hard-facing layer.

Three approaches can be used to produce holes:

Option	Method
Plasma cutting with torch manipulation	Cut a straight hole first, then angle the torch according to the taper of the bolt head
Pre-machined insert	Gouge a hole through the plate, machine a separate tapered insert from ductile steel, place it in position and weld from the rear side
Reverse drilling from the rear side	Drill through the steel backing to near the hard-facing interface, then remove the remaining material from the front using air carbon arc gouging

All three approaches avoid direct mechanical drilling through the hard-facing layer.

6. Burrs must be removed before cold bending

Burrs may be small, but they are located at the edge where tensile stress is high during bending.

A sharp edge projection can become a stress concentration point. If the burr lies on the outer side of the bend, it may become an initiation point for cracking.

Before bending, inspect the edge directly:

Acceptable: the edge has been ground smooth and no sharp projection can be felt by hand
Requires correction: a sharp projection remains and must be ground before forming

This is a simple workshop inspection, but it directly affects the quality of the next operation.

7. Cold bending: determine all required data before forming

Tam-thep-khi-duoc-uon-cong — Steel plate after bending (*Image: SSAB)*

Before bending, at least three conditions need to be determined:

Condition	Requirement
Plate temperature	Bring the plate to room temperature before bending
Minimum bending radius	Refer to the correct material grade and rolling direction
Bending direction	Bending transverse to the rolling direction and parallel to the rolling direction do not use the same radius

The bending direction should be shown on the drawing rather than decided only at the workshop.

Before starting a fabrication batch, the material grade, thickness range and rolling direction of the plate must be available.

If the rolling direction is unknown, there is insufficient data to determine the appropriate bending radius.

If small cracks appear parallel to the bend edge, the component should be reworked according to the applicable requirement rather than being rebent on the same component to correct the angle.

8. The sequence of cutting, bending and drilling depends on component geometry

There is no single sequence that applies to every component.

Situation	Sequence to consider
Component needs to be bent close to the minimum radius	Waterjet cut first, then bend
Component requires a wide bend and complex edge cutting	Bend first, then trim the edge
Hole is close to the bend line	Bend first, then drill

The case of holes located close to the bend line requires particular attention.

If the hole is drilled before bending, it may deform and become an initiation point for cracking. Bending first and drilling afterward helps avoid subjecting the hole to the forming process.

The fabrication sequence should therefore be determined from component geometry and the requirements of subsequent operations, not only from the convenience of individual fabrication equipment.

9. Operations to avoid when cutting and forming high-hardness steel

Several deviations identified in the overview article need to be controlled directly during cutting and forming.

Operation to avoid	Why it matters
Reheating the material independently in the workshop	May alter the material condition and properties established during manufacturing
Bending below the minimum bending radius	Increases the risk of cracking in the bend area
Rebending to correct the angle	The material has already undergone deformation during the first bend, so its condition for the second bend has changed
Bending across an embossed marking	The marking may create a stress concentration zone along the bend line
Returning leftover plate to storage with sharp cut corners	Sharp corners create stress concentration points and should be treated before storage

The common point is that the consequences may not appear immediately after the operation is performed.

A newly completed component that looks normal is not sufficient evidence that all fabrication conditions were appropriate.

Handling and storage of leftover plate after fabrication are discussed in more detail in Part 6: Handling, storage and preservation.

10. Items that can be checked immediately in the workshop

The inspections in Part 1 focus on thermal condition, edge quality and forming conditions.

Item to inspect	Inspection method	Action when unacceptable
Preheating temperature	Contact thermometer, measure both sides	Stop work and reheat according to requirements
Cut-edge quality	Visual inspection, hand inspection and appropriate measuring tools	Rework the edge; if cracking remains, remove the cracked area
Burrs before bending	Hand inspection	Grind smooth before forming
Bending direction	Check against the drawing	Reconfirm before fabrication
Bending radius	Appropriate radius measuring tool	Correct according to the drawing and applicable documentation

These inspections should be completed before the component moves to the next operation.

The objective is not only to identify unacceptable components, but also to prevent a deviation from the cutting stage from continuing into forming, welding or installation.

11. Responsibilities during fabrication

Each operation should have a clearly defined responsible department to prevent technical information from being lost when work moves from engineering to the workshop.

Task	Responsible department/person
Select cutting method	Engineering team, based on the material and subsequent forming requirements
Show bending direction on the drawing	Engineering team
Perform preheating and temperature measurement	Cutting operator, with results recorded as required
Remove burrs before bending	Fabrication operator
Inspect cut-edge quality	Workshop supervisor or designated inspector
Determine the cutting, bending and drilling sequence	Engineering team in coordination with the workshop

The cutting method should be determined from the beginning because it directly affects edge condition and forming capability in subsequent operations.

If the method is selected only for convenience or cost at the cutting stage, additional rework may be required or the component may no longer satisfy the original forming requirements.

12. Items to review before moving to the next operation

Before the component leaves the cutting and forming stage, confirm:

correct material grade and thickness range
cutting method suitable for the material and subsequent forming requirements
preheating requirements identified according to the correct material and cutting technology
actual temperature checked where required by the procedure
cut-edge quality inspected and corrected
burrs removed before bending
plate rolling direction identified
bending direction shown on the drawing
bending radius complies with the applicable technical documentation
cutting, bending and drilling sequence is suitable for component geometry
cracks or abnormal indications have been addressed before moving to the next stage

This review helps prevent a deviation from cutting or forming from continuing into welding, installation or later fabrication operations.

Specific requirements for tolerances, geometry, bending direction and component dimensions must still be checked against the approved fabrication drawing.

13. Scope of application and references

This article identifies principles and control points for cutting and forming. Three points should be noted when applying the information.

First, preheating thresholds, bending radii and the applicable ranges for shearing and punching vary by material grade and thickness. Specific values must be checked against the correct technical documentation for the material being processed.

Second, there is no universal cutting, bending and drilling sequence for all components. The situations in this article provide guidance, but the final decision must be based on the actual geometry and requirements of the component.

Third, this article does not replace the approved fabrication drawing. Permissible tolerances, bending direction and specific requirements must still be shown and checked on the drawing.

EN 10163-2 is referenced for content relating to steel plate surface and edge quality.

Parameters relating to material grade, thickness, cutting method and bending radius must be checked against the manufacturer’s current technical documentation.

The principles concerning operation sequence, workshop inspection organization and handling of field indications are based on Gia Anh’s fabrication experience.