Value Through Solutions®


Flow Drilling Screw Technology

Flow Drill



Installation into aluminum or steel sheets without the need for pre-punched or drilled holes

Hole alignment issues minimized

Chipless thread forming

High safety window between installation and stripping torque

High shear and pull-out resistance

Dynamic in high vibration applications

Compatible with metric machine screws for service


Multiple point designs available depending on application requirements

Head undercut present to capture upward material flow

Unique head-drive combinations for maximum assembly efficiency and fastener weight control


OptiCalc Software validates applications, speeding up engineering development time




FDS Application Testing Equipment

FDS Process Lab Weber Flow Drill Screw

Today’s designers continue to search for ways to maximize product performance and efficiency. One approach that is being taken in the automotive industry and elsewhere is lightweighting. The utilization of thinner and lighter materials like aluminum can bring about significant weight reduction. The joining of these materials is critical to meet or exceed current performance levels. There have been many advancements in fastening technologies for these thin sheet joints. However, the majority of products require two-sided access for installation. The Semblex FDS® flow drill screw was developed as an innovative single-sided fastening solution for these lightweight, thin sheet joints. 

FDS® Features

FDS Featured

FDS® Benefits


  • One-sided access is required for the assembly
  • Pre-drilling or punching of joined material is not required
  • Chip-less forming of female threads
  • Deep extrusion was created, resulting in high thread engagement and joint strength
  • Excellent drive-to-strip differentials for increased safety margins
  • Eliminates welding costs and workplace environmental concerns
  • Standard metric thread screws can be used in repair situations
  • Effectively used with adhesives for an enhanced joint performance

Assembly Process

FDS® Assembly without Clearance Holes

  • No part preparation required like pre-drilling or punching
  • Undercut design required to capture up-flowing material
  • Down-holder (pressure foot) required to resist movement of the top layer

Assembly without Clearance Holes


  1. Warming up the sheet metal by axial end load and high-speed

  2. Penetration into the material

  3. Forming of the extrusion

  4. Chip-less forming of a female machine thread

  5. Installation

  6. Tightening with the pre-set torque


FDS® Assembly with Clearance Holes

  • Beneficial when top layer material is incompatible with the flow drilling process
  • Simplified head design may be used
  • Down-holder (pressure foot) not required


Assembly with clearance holes


  1. Warming up the sheet metal by axial end load and high-speed

  2. Penetration into the material

  3. Forming of the extrusion

  4. Chip-less forming of a female machine thread

  5. Installation

  6. Tightening with the pre-set torque

Assembly Equipment

Fastening Equipment

Fastening Equipment Selection

FDS® assembly requires high-speed automated drive systems that control and adjust speed, torque, axial load, and depth throughout the multi-stage installation process.

Programmed assembly parameters are dependent on the following joint characteristics:

  • Sheet thicknesses
  • Number of layers
  • Material properties
  • Surface treatment
  • Overall joint requirements


FDS® installation equipment is commonly paired with robotics to allow for pre-programmed locating and assembling of joints in various spaces and positions.

Semblex has relationships with several installation equipment manufacturers and integrators that can assist you with selecting, building, and installing equipment.

Test Equipment

Semblex can perform drive testing utilizing a test stand-mounted drive system.

Validation testing can be performed on material coupons to validate the feasibility of different material stacks and to help develop appropriate program parameters.

Tensile test equipment can also gather peel-and-shear performance data.

Please contact Semblex Engineering Services to discuss any testing needs you may have.

Test Equipment


FDS® Designs





FDS logo FDS standard FDS PKS

Material and Heat Treatment 

Case-hardened mild steel
Through hardened steel
Induction hardening

Case-hardened mild steel
Through hardened steel
Induction hardening


Zinc with passivation
Zinc-nickel with passivation
Zinc flake with optional top coats
Others upon request

Additional lubrication is avoided in most applications to ensure the adhesion of cataphoretic coating.


No pre-hole in select layers

Pre-hole in all layers



  0.4 - 1.8 mm


  0.8 - 5.0 mm


  0.8 - 4.0 mm



  0.4 - 1.8 mm


  0.8 - 5.0 mm


  0.8 - 4.0 mm

Stainless Steel

  0.4 - 1.5 mm


Preferable for automated assembly

Tolerance-free assembly because of no misalignment with clearance holes.

Extremely high joint strength

Ideal screw for safe assembly and dynamic loads

Preferable for manual assembly

Due to a bigger clearance hole compared to the smaller pilot hole, some tolerances can be compensated

Low-end load required



Design Guidance

Recommended clearance hole diameter (dD

Flow drilling with the FDS® screw creates an extrusion in both the fastening and driving directions. This material can be contained when using a clearance hole, avoiding the need for undercut head designs. The following are recommended clearance hole sizes. 

FDS® Size 





5.1 - 5.7

6.7 - 7.4

8.2 - 9.1


Recommended clearance hole diameter (d)


Recommended pilot hole diameter (dV) for Type PKS 

The optimum hole diameter depends on the respective range of requirements on the joint and should be specified according to the application. 

FDS® Size 




sheet thickness S2  [mm]


1.5 - 2.0

1.8 - 2.5



1.6 - 2.2

1.8 - 2.5

2.0 - 3.0


1.8 - 2.5

2.0 - 2.8

2.2 - 3.2


2.0 - 2.6

2.2 - 3.0

2.5 - 3.5


2.2 - 2.8

2.6 - 3.4

2.8 - 3.8


2.4 - 3.0

3.0 - 3.8

3.4 - 4.5



3.4 - 4.2

3.8 - 5.0



4.2 - 4.6

5.2 - 5.6






pilot hole diameter for type PKS

Part Length Considerations

Part Length Considerations

Standard FDS® Design 
b = S
1 + 3 x S2 

PKS FDS Design
b = S
1 + 2 x S2 

Part Length Considerations Table


Peel and Shear Performance Comparison

Below, you will find the strength properties achieved from assembling with FDS® fasteners compared to other joining methods. The University of Paderborn in Germany completed tests in high-strength sheet steel. The performance enhancements available when FDS® fasteners are combined with adhesive bonding are also shown. 

Peeling Strength

Peeling strength Fm and energy absorption F0.3*Fm of different joining methods in steel (ZStE 340)


Shearing Strength

Shearing strength Fm and energy absorption F0.3*Fm of different joining methods in steel (ZStE 340)


NOTE: All data tables shown are for guidance purposes only.

Additional Family Products


FastFlow® FDS®
Rapid Flow Drilling Screw Technology

    Data Sheet(s)    

FDS® Flyer     FDS® Brochure.     FlowStud® FDS®