ويسمى بالإنجليزية: (Resistance Welding)، هى إحدى طرق اللحام التي تستخدم فيها الحرارة والضغط وتتولد الحرارة نتيجة لمرور تيار كهربي له شدة عالية وفولت منخفض لفترة زمنية قصيرة محددة في الموضع المراد لحامه من الجزء. وتمم عملية اللحام في النقطة أو المكان الذي ارتفعت حراراته وذلك بالضغط بواسطة قطبية.
تعتبر هذه الطريقة في اللحام من اطرق السهلة في إتمامها وكذلك لها قدرة إنتاجية عالية لذا في تعتبر طريقة اقتصادية بالنسبة لسعر التكلفة لو قورنت بالطرق الأخرى بالرغم من ارتفاع سعر ماكينات اللحام بالمقاومة وتمتاز أيضا أن في هذه الطريقة إمكانية لحام المعادن الغير متشابهة.
تستخدم هذه الطريقة عادة في لحام الألواح الصغيرة السمك للمعادن المختلفة سواء كانت حديدية أو غير حديدية
أنواع لحام المقاومة الكهربية
اللحام النقطي (لحام البقعة)
و يسمى بالإنجليزية(Spot Welding)، وهو أحد الطرق الشائعة في عمليات اللحام بالتلامس وينقسم لحام البقعة إلى مجموعتين:
- لحام البقعة المفردة من جهة واحدة أو من الجهتين.
- لحام البقعة المتعددة، حيث يتم عمل بقعتان أو أكثر في نفس الوقت أثناء تدفق التيار.
اللحام الدرزي (اللحام الخطي)
و يسمى بالإنجليزية (Resistance Seam Welding)، يستعمل هذا النوع في لحام خزانات الزيت والبنزين والماء والمواسير وعدد من الأجزاء المصنوعة من الصلب والمعادن غير الحديدية ويتراوح سمك المعدن الذي يمكن لحامه بهذه الطريقة بين 25-30 مم.
وينقسم هذا النوع من اللحام إلى مجموعتين:
- لحامات التدريز التركيبية.
- لحامات التدريز التقابلية.
Resistance Seam Welding is an extremely efficient joining technique ideally suited for high-volume manufacturing, adaptable for most metals and their alloys.
Resistance welding uses the application of electric current and mechanical pressure to create a weld between two metallic parts. Copper electrodes conduct a current through the work pieces, generating enough local heat from the electrical resistance and the thermal conductivity of the metal to create a small molten pool. The metal then cools while under pressure, forming a weld nugget with adequate strength to hold the parts together. The process requires the application of external force, but no fluxes, filler metals, or external heat sources are necessary
Resistance Seam welding is a high-speed resistance welding process that produces leak-tight, continuous joints for sheet metal applications. In seam welding, the sheet metal parts are clamped between rotating wheel electrodes that transmit continuous pulses of electrical current while advancing the work piece, forming a series of overlapping weld nuggets.
Resistance Seam Welding Benefits
- Efficient energy use, with little pollution
- Fast processing times
- Easily automated
- No required filler materials
- Economical
- Adaptable to a variety of electrically conductive materials
- Ability to produce leak-tight welds
Resistance Seam Welding Limitations
- Applications may be limited by component shape and wheel access
Vollrath, a full-service, ISO 9001:2000 certified company, has the manufacturing strength, technical knowledge, and experience to hold the leading edge in welding services. Our attention to process control eliminates common production problems and ensures the delivery of consistent quality for every welding application.
For more information about our resistance welding capabilities or to request a quote for your specific application, please contact Vollrath. We’d enjoy hearing from you.
by Steve Westgate
Description
The seam welding process is an adaptation of resistance spot welding and involves making a series of overlapping spot welds by means of rotating copper alloy wheel electrodes to form a continuous leak tight joint. The electrodes are not opened between spots. The electrode wheels apply a constant force to the workpieces and rotate at a controlled speed. The welding current is normally pulsed to give a series of discrete spots, but may be continuous for certain high speed applications where gaps could otherwise occur between individual spots. Seam welding equipment is normally fixed and the components being welded are manipulated between the wheels. The process may be automated; it is illustrated in Fig.1.
 | Fig.1. Conventional wide wheel seam welding |
Current status
There are a number of process variants for specific applications:
Wide wheel seam
- Wheel contact width normally 5
t mm flat (where t is single sheet thickness in mm).
- General purpose welding (domestic radiators up to about 6 m/min).
 | Fig.2a) Wide wheel seam |
Narrow wheel seam
- Wheel contact shape typically 6mm radius.
- Knurl drive on wheel edge with contact surface continuously planished.
- Controls electrode contamination when welding coated steels, such as for vehicle fuel tanks.
 | Fig.2b) Narrow weld seam |
Consumable wire seam welding
- Shaped, consumable copper wire fed between the wheels and sheets to be joined to give consistent clean contact.
- Used for welding coated steels such as tin cans and vehicle fuel tanks.
 | Fig.2c) Consumable wire seam |
Mash seam welding
- Narrow overlap of sheet edges, which are partly crushed together during welding.
- High speed welding of tin cans and drums (0.2mm tinplate up to 100m/min).
- Wide wheel or consumable wire processes used.
 | Fig.2d) Mash seam welding |
Foil butt seam welding
- Foil welded on to each side of the butted edges of the sheets to be joined.
- Typically 4mm wide stainless steel foil used to preserve corrosion resistance on coated steel.
- Virtually flush finish with no crevice and used to produce wide panels.
 | Fig.2e) Foil butt seam welding |
Important Issues
The main issues concerning seam welding are in weld quality control and welding speeds.
- High speed welding of coated steels is of particular importance in manufacture of tin cans. Specialist consumable wire seam welding machines are used. Quality monitors have been developed for these applications and welding speeds up to about 100m/min are possible. Steels with alternative coatings to tin, for canning applications, present difficulties due to their high surface resistance.
- Weld quality is controlled mainly by tight process control together with periodic testing of samples. Factors such as material and pressing quality, and alignment of the electrodes to the material, are critical to achieve high speed, quality welding, for example in coated steels for fuel tanks.
Benefits
Seam welding enables high welding speeds to be obtained compared with many other techniques, but can be limited by component shape and wheel access.
Risks
There are some limitations on material weldability but attention to correct setting up and good process control can solve most production problems. The main hazards are: (i) the risk of crushing fingers or hands; and (ii) burns or eye damage from splash metal. Little fume is produced but may need attention when welding coated steels or when oils or organic materials are present.
