Hot Plate Welders


Hot Plate
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Hot Plate welding is widely used for the most challenging materials and large part assembly with high strength and hermetic requirements. During the hot plate welding, both part halves are held rigidly in position against/near a thermally heated platen to melt the joining surfaces. The materials are then quickly separated from the heated source and driven together and allowed to re-solidify under pressure.

Forward has manufactured hot plate systems since 1965. Our experience has resulted in the design of equipment based on ultra-rigid construction and detailed melt control to ensure precise repeatability of part quality, year after year of production.

Vertical or horizontal platen configurations are available. From manually loaded and unloaded machines to semi and fully automated in-line systems, Forward offers the widest array of standard products designed to accommodate a most product sizes.

Hot Plate Welding Process Advantages

  • Ability to weld large parts and complex shapes and compound contours with little regard to part and joint geometry.
  • Can weld tall, thin, non-supported interior walls.
  • Highest joint strength of any weld process when welding PP,PE, TPE and EPDM materials.
  • Significantly smoother flash with less particulate than other assembly methods such as Vibration Welding.
  • Compatible with most thermoplastics.
  • High strength, hermetic welds are typical.
  • Multiple parts per cycle can be welded.
  • Easily automated.
  • Relatively low equipment cost.
  • Nature of the process is simple and highly forgiving of part tolerances when compared with other assembly processes.

About Hot Plate Welding
Designing for Hot Plate Welding
Hot Plate Weld Tooling
Hot Plate vs. Other Welding Methods


About Hot Plate Welding

Hot Plate Welding is a thermal welding technique capable of producing strong, air-tight welds in thermoplastic parts.  When using thermal energy in a tightly controlled manner, thermoplastic parts can be heated to molten temperatures very quickly and then joined together.

Thermal heat is introduced to the interface of each part half by a precision temperature controlled platen consisting of multiple uniform temperature distribution cartridge heaters.

Hot Plate Welding Process:

 Hot Plate Process StepOne

Step One

Part halves are placed into and securely gripped by precision holding fixtures which insure adequate support and accurate alignment of the part halves throughout the hot plate welding process.

 Hot Plate Process StepTwo

Step Two

To heat the part joint area, a thermally heated platen is placed between the part halves.  The holding fixtures close to compress and melt the part halves to be welded against the platen, displacing material at the joint area only

 Hot Plate Process Step Three

Step Three

Compression and material displacement continue until precision hard-stops built into the tooling are met.  Thermal heat continues to conduct into the material even though compression and displacement have stopped.

 Hot Plate Process Step Four

Step Four

After the joint area reaches molten temperature, the holding fixtures open and the heat platen is withdrawn.

 Hot Plate Process Step Five

Step Five

The holding fixtures then close, forcing the two parts together until hard-stops on the holding fixtures come into contact with one another.

 Hot Plate Process Step Six

Step Six

When cooling is complete, the gripping mechanism in one of the holding fixtures releases the part, the holding fixtures open and the finished part may be removed.


Our existing line of hot plate welders is extensive. Vertical or horizontal platen welder configurations are available (see below).  From manually loaded and unloaded machines to semi and fully automated in-line systems, each of our hot plate welders is designed to accommodate a specific range of application requirements.

Vertical vs. Horizontal Platen Systems:

Vertical

Horizontal

Easy to manually load both part halves positively into the tooling, ensuring precise, repeatable alignment during welding.More difficult to manually load both part halves positively as access to upper tool can be ergonomically challenging.
Not ideal when internal componentry is loose inside the part halves prior to welding.
Ideal system for part designs where internal components are loose inside the lower part half prior to welding.
No simple option for operator to load part halves outside the machine.Allows option of manually loading part halves outside the machine (requires drawer load and automatic top-half part pick-up).
No special location features need be designed into the part halves or tooling for accurate alignment.
Requires special location features be designed into molded parts themselves or the tooling (increases tooling cost/complexity) when using automatic top-half parts pick-up.
Faster tool changeover than most horizontal machines offered today.Slower tooling changeover typically.
More complex to automate (often requires roboticaction).
Very easy to automate when optional drawer load and automatic part drop to conveyor belt is used.
Not ideal for automatic part drop (onto conveyor belt) after welding.Allows easy automatic part drop onto conveyor belt after welding (when equipped with optional drawer load).
Twin motion (left and right) fixturing allows independent control of force/speed on each part half, both against heat platen and against each other.Single motion (upper only) fixturing allows independent control of force/speed of upper part half only.

Critical Hot Plate Welder Parameters:

Time and Temperature:

The platen temperature to melt the part interface depends on the type of plastic being joined. Each thermoplastic has a characteristic melt time/temperature curve, and a weld can be produced at any temperature on the curve. Typically the highest possible temperature at the shortest time is selected to minimize cycle times.The typical hot plate temperature range is 300° to 950°F.

Hot Plate Time/Melt Diagram

Types of Hot Plate Welds:

Low Temperature

  • Temperatures less than 500°F
  • Low temperature tools require Teflon coated heat platen inserts or Teflon cloth.
  • Typically coating/cloth needs replacement every 1500-8000 cycles.
  • Used on Medical Applications even with High Temp materials to eliminate contamination / discoloration / maximize weld strength.
  • Typical cycle time is 20-40seconds.

High Temperature

  • Temperatures higher than 500°F
  • High temperature tools are typically manufactured using P-20 tool steel.
  • No melt release coatings typically required
  • Melt residue smokes away or requires brush cleaning(Nylon)
  • Smoke/Fumes present: requires exhaust/smoke removal or aircleaning
  • Typical cycle time is 10-30 seconds.

Non-contact

  • Typically temperatures higher than 900°F
  • No residue on platen.
  • No material discoloration.
  • Precise molding tolerances required.
  • Not limited to flat mating surfaces.
  • Typical cycle time exceeds 40 seconds.
  • Technique is most complicated and least often used in production hot plate welding.


High Temp vs. Low Temp Hot Plate Welding:

HIGH TEMP CONTACT WELDING

(above 500°F)

LOW TEMP CONTACT WELDING

(500°F or less)
Faster cycle times:
  • 15 to 45 seconds typical
Slower cycle times:
  • 30 to 60 seconds typical
No coating required. Residue smokes off through Exhaust Fan. Lower maintenance.Teflon coating or Teflon Coated Fiberglass Cloth required on heat platen or insert surface. Higher maintenance.
Process works well for a variety of materials (some limitations).
Process works well for a variety of materials (some limitations).
Process can join certain dissimilar materials (wider range).
Process can join certain dissimilar materials (limited number).
Not ideal for welding Polyethylene (material excessively sticks to the heat platen core).
Ideal for welding Polyethylene.
Easy welding of Polypropylene.
Can weld Polypropylene (low temp required in Medical Cleanroom environment).
Highest strength when welding Nylon. Involves ultra high-temperature heat platen cores which must be scrubbed with metal brushes every cycle to clean off build-up of residual material.
Lower strength when welding Nylon (temperature too low).
Fillers in the material can build up on the heat platen requiring periodic cleaning (automatic cleaning systems are available on several models).Fillers in the material seldom cause need for increased cleaning as buildup only occurs when Teflon coating/cloth needs to be changed.
Smoke and fumes are common as residue is burned on heat platen core between cycles (ventilation may be required). Virtually no smoke or fumes during welding process at low temp.


Contact vs. Non-Contact Hot Plate Welding:

CONTACT WELDING

(High or Low Temp)

NON-CONTACT WELDING

(Very High Temp above 900ºF)
Faster cycle times:
  • 15 to 60 seconds typical
Slower cycle times:
  • 30 to 90 seconds typical

Higher Maintenance. Teflon coating or Teflon Coated Fiberglass Cloth required on heat platen or insert surface with some materials. Some fillers in high temp materials leave residue on platen which must be brushed/wiped several times per day.
Lower Maintenance. No coating required regardless of the material to be welded.
Parts can be welded without absolute precision as joint surfaces will be made parallel to one another during melt phase when polymer is making contact with heat platen.
Parts must be molded more precisely as there is no contact based melt step to flatten/parallel joint surfaces.
Flash traps may be required for cosmetic applications when welding with contact.
Due to limited displaced material, flash traps are often not required.
Temperatures typically below 900ºF.  Limited risk of thermal damage to non-joint areas of parts in close proximity to heat source.
Temperatures often in excess of 900ºF.  High risk of thermal damage to non-joint areas of parts in close proximity to heat source.

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Designing for Hot Plate Welding

Hot Plate Weld Strength:

The hot plate welding process produces a welded joint which, in many cases, yields a weld strength that is consistently equal to or stronger than any other area of the part. As a result, the weld area can most often be exposed to the same strains and stresses as any other area of the part.

Common Hot Plate Welded Materials:

Hot Plate Welding Joint Designs:

Hot Plate Joint Unwelded                       Hot Plate Joint Welded

Typical total material displacement is 0.060". The 0.030" material displacement per side includes 0.015" for material and 0.015" for seal. This may vary depending on part material, geometry, and molded part flatness.  We strongly recommend discussing your joint design with one of our application engineers before arriving at your final part design.
Common Joint Designs for Hot Plate Welds

Other Hot Plate Welding Design Considerations:



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Hot Plate Weld Tooling

Hot Plate Tooling Diagram

Advantages of Forward Technology Hot Plate Tooling:

  • Over 95% of all tooling is designed and manufactured for your application by our in-house Tooling Design and Fabrication department in Cokato, MN.
  • This in-house capability insures optimal quality and scheduling control as well as reducing time requirements in the event of product design changes. 
  • No charge/obligation complete application review and joint design assistance.
  • Full prototyping capability.
  • All tools are designed for ease of maintenance, adjustment, and maximum life.
  • Tools provide support and location of joint area as well as accurate alignment throughout the welding process.
  • Virtually all tools are thoroughly tested and debugged at our facility on equipment in our laboratory.
  • Tools can be designed for use with Forward Technology or most competitor's welders.
  • Full start-up service/support at your facility is available.

Standard Hot Plate Tooling:

  • Precision CNC cut holding fixtures supports joint area of each part half.
Lamp Contoured Hot Plate Holding Fixture
  • Holding fixtures can be split if necessary to accommodate part-to-part variations or for welding warm/hot parts.
Hot Plate Holding Fixture Split for Adjustment to Warm Parts
  • Hardened steel fixture top plates (metalized by black oxide, chrome plating or anodizing)
Lamp Housing Hot Plate Holding Fixture
  • Steel, aluminum, urethane, or acetal tooling components.
  • Lightweight auminum backing plates
  • Heavy-duty slides used for support & part retention in areas where clearance is needed for loading & unloading.
Coolant Reservoir Hot Plate Tooling w-Grippers
  • Custom grippers and vacuum cups used to secure parts in holding fixtures.
Pallet Hot Plate Holding Fixture
  • Mechanical positive hard-stops on each fixture and heat platen.
    • Control depth of melt and weld/seal dimensions.
    • Provide assembled product consistency
    • Eliminate risk of cold joint (all molten material being extruded from joint by excess travel)
    • Adjustable for part to part variance
Hot Plate Tooling Hard-Stops
  • Precision cartridge heaters contained with heat platen assembly designed for uniform temperature distribution.
Flat High Temperature Heat Platen                           Contoured High Temperature Heat Platen
  • Teflon coated fiberglass cloth or Teflon coated inserts to prevent material adhesion to heat platen on low temperature applications.
Heat Platen with Insert

Minimal Tooling Contact Hot Plate Holding Fixtures:

Lamp Lens Hot Plate Holding Fixture
  • Nests are CNC-machined aluminum to match part contours.
  • Nest tooling is designed to minimize risk of blemishing Class-A molded parts – part is supported in fixture tooling primarily only under the weld bead, and adjustable locators allow optimizing fixtured product position consistency.
  • All product support fixture surfaces that are unnecessary for proper support or product location are relived ¼ to 3/8” from the part.
  • Gripping of only edges of lens.
  • Vacuum Cup-Only contact will protect and locate Class-A surfaces.

Hot Plate Tooling Options:

  • Part presence sensors verify part presence/position prior to allowing machine to cycle.
  • Part eject eases removal of welded parts from tooling.
  • Quick change system for customers using multiple tools in one machine.
  • Tool coding utilizes RF Tagging to automatically identify the application and select the correct program/setup.
  • Pre-heat station allows pre-heating a heat platen prior to installation to minimize tooling change over time. 
  • Heat platen & tooling fixture cart with casters for storage and easy relocation of heat platen assemblies and tooling.

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Hot Plate vs. Other Welding Methods

Hot Plate vs. Infrared Welding

HOT PLATE WELDING

INFRARED WELDING

Accurate part temperature control based on feedback from thermocouples into temperature controllers.
Highly accurate part temperature control based on utilization of Phase Angle Control type logic and Power Control (line/load regulation) Transformers
Temperature control not easily affected by voltage.  Feedback from the thermocouples built into the heat platen allow the system to correct for variable incoming voltage.  Power Control Transformer not required even when incoming voltage varies.
Temperature control requires constant incoming voltage as system does not allow for readily available feedback from output/tooling.  Correction for varying incoming voltage (5% or more) requires costly Power Control Transformer.
Warm-up time (Preheating) required for roughly 20-40 minutes prior to start of production. Tool changes often require cooling of the heat platen to tolerable temperatures prior to changing tooling.
Instant on/off design requires no warm-up time (pre-heating) and allows faster tooling changeover (no cool-down required).
Higher power requirement.  Heaters constantly pulsing on/off throughout day to constantly maintain temperature.
Lower power requirement.  Higher power drawn only when IR turned on.
Much lower cost system overall.  Constant voltage transformers not required as heat platen incorporates temperature controllers which provide feedback of actual platen temperature.
Cost increase up to 60% or more dependant on emitter design (custom vs. standard) and whether or not Power Control Transformers are needed.  Incoming voltage variances can create IR output density changes which are not readily apparent to the equipment via feedback.
Typically, heat platens are designed for optimal temperature distribution for each application, often requiring an optimized heat platen with each tool.
Very cost effective when designing a common emitter platen and change of masks only.
Cartridge heaters also require replacement although the replacement cost is very inexpensive by comparison with Infrared emitters.
Emitters last only a few years and are very expensive to replace.
Flash traps may be required for cosmetic applications when welding with contact.
Due to limited displaced material, flash traps are often not required.
Parts can be molded without absolute precision as joint surfaces will be made parallel to one another during melt phase when polymer is making contact with heat platen.
Parts must be molded very precisely as there is no contact based melt step to flatten/parallel joint surfaces.
If required to run at low temperature, Teflon coating on heat platen must be moved (sheet) or replaced (coatings)
No need for replacement inserts/coating materials.
Materials such as polyethylene, acetal, nylon and polycarbonate will require release coatings between polymer and heat platen.
Greater design flexibility in materials (all non-contact).
Clear materials and polycarbonate are easily weldable without complexity although some may require release coatings between polymer and heat platen.
Not ideal for clear materials (particularly polycarbonate).
Heat platen temperature distribution is affected by convection currents.
Convection currents not a factor unlike HP welding.
Smoke produced at temperatures above 500ºF only.
High amount of smoke created during the process.
Typically standard “off the shelf” parts are used with no leadtime issues on wear-item parts.
If Custom emitters are used, customer MUST purchase spares immediately as leadtimes for replacements are up to 6 weeks.

Hot Plate vs. Vibration Welding

HOT PLATE WELDING

VIBRATION WELDING

Slower cycle times:
  • 15 to 45 seconds (high temp) typical.
  • 30 to 60 seconds (low temp) typical.
Faster cycle times:
  • 8 to 15 seconds typical.
Can weld tall, thin, non-supported inside and outside walls.
Cannot weld tall, thin, non-supported either:  a) inside walls or b) outside walls perpendicular to the direction of vibration.
Direct control of temperature at weld joint.
No direct control of temperature at weld joint.
Process works well for a variety of materials (few limitations).
Process works well for a variety of applications (some limitations).
Complex to weld Nylon.  Involves ultra high-temperature heat platen cores which must be scrubbed with metal brushes every cycle to clean off build-up of residual material. Yields the strongest bonds compared to most other welding methods.
Easy welding of Nylon.
Almost no part size limitations.
Can be difficult to weld VERY large parts.
Higher joint strength with Polypropylene and Polyethylene as the process heats the interface without friction.
Lower joint strength with Polypropylene and Polyethylene due to absorption of vibration within the material instead of transfer to the joint area.
Fillers in the material can build up on the heat platen requiring periodic cleaning (automatic cleaning systems are available on certain models).
Fillers in the material are not a problem.
Process can join certain dissimilar materials (limited number).
Process can join certain dissimilar materials (limited number).
Can weld parts with contours in both directions.
Can weld parts with contours in one direction only.
Weld plane limited to 45° maximum from flat plane.
Weld plane limited to 10° maximum from flat in the axis parallel to vibration.
Less sensitive to molded part variations.
More sensitive to molded part variations.
Lower initial capital equipment costs.
Higher initial capital equipment costs.
Higher tooling costs (requires heat platen).Lower tooling costs (no heat platen required).
Process requires a heat platen assembly.
Less complex tooling.
Heat platen maintenance; replace heaters and Teflon inserts when using low temperature.
Lower tooling maintenance.
Slower tooling change-over times; also may have to change heat platen and allow for heat up.
Faster tooling change-over times.
Process creates solid, smooth flash bead with virtually no particulate.
Process can create flash that can break off causing loose particles (application and material dependant).
Virtually no smoke or fumes during welding process at low temp; will create smoke and fumes when welding at high temp.
Virtually no smoke or fumes during welding process.
Higher power consumption (required for heaters).
Lower power consumption (no heat platen heaters).

Hot Plate vs. Electromagnetic Welding

 HOT PLATE WELDING

ELECTROMAGNETIC WELDING

Slower cycle times:
  • 15 to 45 seconds (high temp) typical
  • 30 to 60 seconds (low temp) typical
Faster cycle times:
  • 5 to 15 seconds typical
No consumables required.
VERY EXPENSIVE consumable required (proprietary ferro-magnetic material).
No additional process steps required.
Additional and very critical process step required (installation of consumable ferro-magnetic material).
Melt areas limited to sections where heat platen can contact.
Ideal for melt areas that are difficult to weld with any other technique (last resort).
Parts can be molded without absolute precision as joint surfaces will be made parallel to one another during melt phase when polymer is making contact with heat platen.
Parts must be molded very precisely as there is no contact based melt step to flatten/parallel joint surfaces.
Limited risk of thermal damage to non-weld areas.
No risk of thermal damage to non-weld areas. Heat remains in ferro-magnetic component area (joint) only.
Moisture introduced to welded part has no effect on part appearance.
Moisture introduced to welded part can result in rust residue on parts.
Accurate failure/problem diagnosis can be performed by virtually any maintenance technician.
Accurate failure/problem diagnosis requires extensive knowledge of RF generators.
Replacement parts largely off-the-shelf items.
Requires replacement of special expensive RF Oscillator tubes every few years.
Joint line contour limited to 45° from flat plane before weld strength is drastically impacted.
Joint line contour almost unlimited (provided RF tooling can remain in roughly equal proximity to other melt areas)
Metallic components can be installed prior to welding.
Metallic components should be installed only after welding due to possible magnetic heating in undesirable areas during the electromagnetic welding process.
Defect parts can be recycled easily as no foreign matter exists in the joint area.
Defect parts cannot be recycled easily due to ferromagnetic material within the parts.
Process has virtually no effect on surrounding equipment.
RF emissions can cause interference in surrounding equipment (particularly low control voltage circuitry…UPS scales, PA Systems, machines with servo motors)
Periodic heat platen maintenance required; replace heaters and Teflon inserts (when using low temperature).
Lower tooling maintenance.
Lower initial capital equipment costs.
Higher initial capital equipment costs due to requirement of RF Generator.
Higher tooling costs (heat platen).
Lower tooling costs (no heat platen required).
Slower tooling change-over times; also may have to change heat platen and allow for heat up.
Faster tooling change-over times.

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