TEM method

TEM APPLICATIONS / INDUSTRIES

Thermal deburring (TEM - Thermal Energy Method) is a process for removing production-related burrs from a wide variety of machine parts, e.g. by milling or drilling. Scientifically correct, TEM is referred to as a "thermal-chemical deburring process" and, according to DIN 8590, is assigned to the subgroup of ablative processes "chemical ablation".

In the TEM process, the material to be removed is burnt because a chemical reaction takes place between the material and the gas mixture.

For this purpose, the workpieces are placed in a bell-shaped deburring chamber which is closed hydraulically by means of a sealing plate. A precisely defined mixture of fuel gas and oxygen is fed into the deburring chamber via a gas dosing system and will be ignited. During the subsequent combustion, temperatures of 2,500-3,300 °C are generated. The burr to be removed reaches its ignition temperature and reacts with the excess oxygen in the deburring chamber. This leads to a complete combustion of the burrs within 20 ms.

Various metallic materials as well as all thermoplastics such as PA, PE, PTFE, PUR and PMMA, but also injection moulded parts without glass fibre content can be processed. The cycle time for thermal deburring is less than two minutes.

Zahnräder thermisches Entgraten

ADVANTAGES OF THERMAL DEBURRING

  • Uniform deburring of all outer and inner burrs in one operation, process reliability
  • Process does not influence the surface structure (plastic parts are smoothed)
  • Deburring result from sharp-edged / burr-free to slight edge rounding is depending on material
  • Unmatched cleanliness and fast cycle times
  • Suitable for high quantities, low energy costs at the same time
  • No wearing tools
  • Simple workpiece fixtures
    • Component geometry plays a subordinate role
    • Also suitable for bulk material

COLOURS OF THERMAL DEBURRING

The colours of the thermal deburring of ferrous materials are derived from the various process stages.

  1. Untreated workpiece
  2. Workpiece after the first shot with Oxygen surplus
  3. Oxide minimization by means of stoichiometric gas mixture (second shot)
  4. Washed workpiece

Depending on the material, the washing of the TEM processed component is an important part of the after-treatment.

Die Farben des thermischen Entgratens

METALLIC MATERIALS

Basically, oxidizable metals can be deburred. However, there are restrictions for commercially available materials:

  • Magnesium, as this material has a tendency to uncontrolled, further combustion due to its low ignition temperature, melting point and boiling point.
  • Titanium, due to very high boiling point (3,535 °C)
  • The same applies to highly heat-resistant materials for aerospace engineering (e.g. zirconium).
Metallische Werkstoffe
Designed bylegereek / istockphoto.com ID: 177331915 / (2013/08/19)

THERMOPLASTIC MATERIALS

As a rule, all thermoplastics can be processed. However, the burr is melted off and not oxidized. Only pure thermoplastics are suitable. Plastics with a glass fibre content are of limited suitability.

During deburring, the burr melts slightly more than the glass fibres, so that the edge looks jagged when viewed microscopically. The roughness of the burnt edge can also be felt with the fingers. Thermosets, on the other hand, cannot withstand the explosion pressure due to their brittleness and burst.

Thermoplastische Werkstoffe
By ratmaner / shutterstock.com Royalty-free stock photo ID: 471679226

THE LIMITS OF TEM

The range of application of “thermal-chemical deburring” is limited by various factors. The material from which the components are made and the size of the burrs limit the application possibilities of the process. The thermal load of the workpiece to be deburred depends on the required deburring quality; normally it will not exceed certain limits.

The burr formation must be designed according to the material. This means that ferrous materials with poor thermal conductivity may have a stronger burr formation than light metals with exactly opposite properties.

The material shall be oxidizable. Exception: plastic, here the burr is melted off.

The workpiece must only be as large as fits into the currently largest deburring chamber. Thanks to the variable chamber dimensions of the iTEM thermal deburring systems, components of the most varied dimensions can be processed. Not only the standard series provide a certain flexibility. Special deburring chambers can often be developed for components with special requirements due to their dimensions. These special machines then enable thermal deburring of, for example, heating circuit manifolds from the sanitary sector or long components from the automotive industry.

Die Grenzen von TEM
By Tashatuvango / shutterstock.com Royalty-free stock illustration ID: 517202785

METHANE, NATURAL GAS OR HYDROGEN CAN BE USED AS FUEL GAS FOR THERMAL DEBURRING.

The machine can be supplied with fuel gas and oxygen in various ways. There are three types of supply:

  1. Gas and oxygen bundles
  2. Natural gas compressors and
    oxygen bundle
  3. Natural gas compressor and oxygen tank
Thermisches Entgraten
By LPW-Reinigungssysteme Riederich

Post-processing

Since the burnt material is deposited on the entire surface of the component in the form of iron oxide after the TEM process, further processing of the workpieces is usually necessary. Exceptions exist if the components are subsequently galvanized, hardened or nitrated.

For steel and iron casting parts, a suitable washing technique should be applied promptly – between 1 and 3 days. If the iron oxide remains on machined surfaces for a longer period of time, rust scars may form. The following cleaning techniques can be used:

1. pH-neutral cleaning with ultrasonic support

In so-called single-chamber systems, the components are placed in baskets and cleaned in a pH-neutral full bath with ultrasonic support, whereby they are additionally sprayed off with high pressure (16-18 bar). The workpieces are then passivated and dried in a vacuum. This technology has become established worldwide in recent years and is particularly noteworthy:

  • Due to lower energy costs – compared to pickling with acid – the higher machine costs pay for themselves.
  • PH-neutral cleaners clean reliably from 40 °C, acid only from 60-70 °C

2. The components are treated in a bath of phosphoric and sulphuric acid. This method is effective, but also has some disadvantages:

  • Heavy pollution for humans and the environment
  • High disposal costs
  • Possible consequential damage to the component due to acid residues
  • Hydrogen embrittlement cannot be excluded.

In the case of workpieces made of aluminum and zinc die-cast, the application of the component is important with regard to post-treatment. Many components are ready for installation after thermal deburring. If, however, the customer demands a low residual dirt content, as for example with pneumatic valves, cleaning is essential.

ARE THERE STILL QUESTIONS?

What are the main advantages of TEM deburring?
The TEM process is one of the fastest and most cost-effective removal processes in which high quality and repeatability are achieved. Burrs, adhering particles and deposits are reliably removed. The machining of a complex or many smaller components is possible after a short changeover time.

What influence does the process have on threads?
Thermal deburring produces a clean, tight and easy to assemble thread. The leading edge, which often breaks or lifts off and damages seals, is deburred. The threads are neither rounded, flattened nor affected on the surfaces.

Can the workpieces be damaged by thermal deburring?
In the case of smaller components, the process reaction can cause the workpieces to collide and be damaged. To avoid this, the components are picked up in fixtures. Larger components, such as hydraulic blocks, can usually be machined without a fixture.

What are the main applications of TEM?
The primary areas of application are cast and turned parts as well as distributor blocks. Through the process, considerable savings can be achieved on bodies for hydraulic and pneumatic valves, as well as castings with internal bore intersections. For zinc die-cast parts, the removal of machining and casting burrs occurs simultaneously. In addition, precision turned and milled parts can be deburred in a matter of seconds using TEM.

Is further treatment of the workpieces after deburring necessary?
As a rule, the components must be post-treated. After thermal deburring, the burnt material deposits on the material surface in the form of iron oxide. Since it is both optically and functionally disturbing, it must be removed. It can only be dispensed with if the components are subsequently subjected to galvanic treatment.

Which areas of the component can be deburred?
The energy carrier of the process is gas, which is distributed evenly within the deburring chamber and the workpiece. For gas, especially under pressure, no opening is too small to penetrate. This means that gas flows around every machining burr, every edge, every shape burr and every particle.

Can all metals be processed equally well?
The deburring success depends on the thermal conductivity and the specific heat absorption of the metals. Ferrous materials as well as metals such as aluminum and zinc alloys can be processed particularly well. Stainless steel can also be processed, but with limitations, by thermal deburring.

Can casting and machining burrs of plastics be removed?
In principle, thermal deburring of plastics is possible. Due to low gas pressures and process temperatures, as well as low melting points of thermoplastics, the process requires special parameters for low energy densities. The thermal deburring machines from ATL are equipped with high-quality control technology so that the processing parameters for thermoplastics can be set sensitively and reproducibly.

What is the workpiece temperature after TEM ?
Components made of steel reach temperatures in the range of 130-150 °C, components made of aluminum reach temperatures of approx. 60-90 °C. The temperature of the components is determined by the temperature of the material.

Which fuel gases can be used?
The fuel gases that can be used for the TEM process are methane, hydrogen and natural gas. For the latter, a natural gas compressor is additionally required.

Can edges be rounded by the process?
Thermal deburring is a non-selective process. Although a light edge deburring process is possible. Rounding can be achieved, but a targeted control of edges is not possible.

Can the deburred edges be kept sharp by the process?
The process can be adjusted so that the edges are deburred and remain sharp.

What influence does thermal deburring have on small bores?
Small holes are deburred just as reliably as other areas.

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